Well... Diplomacy brings a lot of cool things to multiplayer, but one of the most important, is pacts.
The problem is, you can only form any given pact with one other player... so you need to think about who on your team would benifit most from a given pact. So.. if your in econ spot... who do you send out your costly diplo cruisers to to pact up with? for example, that beam pact isnt very helpfull to that tec player, and his missle pact isnt very usefull to you... but it is VERY usefull to that vasari player on your team.
One thing that should be noted: if you form pacts with a race the same as you, you take away alot... think about this... your tec, and you form a metal pact with your tec ally... VS both of you instead form pacts with your non-tec allies... do the math... 2 players get the metal pact bonus vs 4 players. Sometimes the best option is to form pacts with your own race, depending on the situation and how things are playing out, but given equal choices, you should choose the player of a different race to pact with.
Metal pact: It should be preety obvious who you should pact with... the guy with alot of volcanic planets... or, the vasari player with all of his neutrals. pact with the guy with the number one in metal production!
Trade pact: just like the metal pact, this time pact with the guy with a zillion trade ports. Creating these economic pacts with the guys already best in econ means that you get the highest possible gain in resources/second from them.
Missle pact: Give this pact to a vasari player! they have so many units with missles its not even funny! DONT give this pact to an advent player, they have no missles! If your advent and a tec player on your team is trying to form a missle pact with you... accept it (so they get the bonus), but remind them that as soon as get enough relationship with a vasari player they need to switch the pact to that vasari player.
Seige pact: not the most usefull pact... however, the advent generally suck at seige, so this may just help them out a bit (the vasari just suck the planets dry) If you have an AI on your team, this means that thier seige frig spam might do abit of something... not really.
Armor pact: godly pact, great for anyone really, but benifits the Vasari a bit more than the advent, due to te advent's very low hull strenght. If there is a vasari player doing a lot of figthing give it to him, but if your biggest fighters are advent, you may want to give it to them instead.
Supply pact: THis is best given to someone with a low fleet supply limit.... (so they dont have to totally lose thier economy to fleet up) or a vasari with returning armada.
In general,TEC pacts benifit the VASARI more than the advent, so if you only have the diplo cruisers to form friends with one person, you prolly want to make it a Vasari player.
Research pact: get this to someone early, 10% off is a nice little bonus, for both of you. This could really help a tec or vasari friend get some of those nice tier 8 techs. Give this pact to whoever is kinda in an econ spot so they can research the end game stuff (and more pacts!)
Culture pact: preety pathetic as far as pacts go. Give to a player who is on the defencive to allow them to have a better chance of defending with thier culture bonus, and that + antimatter bonus of the tec is preety awsome.
Antimatter pact: The vasari player on your team could prolly use this a bit better than the tec player, thanks to the tec player's kick arse culture bonus. 20% more antimatter means 20% more subversion, 20% more reactive nanites, 20% more repair field, 20% more everything. However, it also is very nice for the tec player as well... if you see a tec player wh 3 donovs, know that those capial ships are almost invinsible untill they run out of antimatter. Makes fluxfield+gauss railgun that much better, and makes those hoshikos 20% more usefull. This pact is also VERY usefull to carrier cruisers. Give this pact to whoever is fighting alot, and/or whoever has alot of support units.
Beam pact: Not very usefull. If there is a advent who does not have the resouces to make his own diplo cruisers, give this pact to him. gives a small boost to a few vasari cap ships, and not much at all to the tec.
Anima pact: this pact is the most amazing pact out there, if your into strike craft. This benifits the vasari much more than the tec. A Vasari bomber squad gains 66% more bombers! and 40% more fighers... compared to 40% more bomber for tec, and 28% more fighers.
Shield pact: the main gem here is that +2% mitigation, which is amazing. This actually rather benifts both other races preety eqeally, prolly best given to whoever has the most capital ship dependant fleet, cause that 2% really helps those capital ships not die... and tec tends to rely on thier capital ships a bit more than the vasari.
In general, advent pacts could go either way, pick the best, closest non-advent team mate you got, and beef em up.
Resource pact: Give to the player harvesting the most resources!
Phase drive pact: That -50% am usage when warping is AMAZING. give this to whoever seems to be on the move the most... which is generally the person on your team who is attacking. Stacking this with the advent AM conservation tech, makes advent very scarry.
Nano tech pact: The tec have alot of hull, so this clearly benifits them the most.
tactical pact: This pact may seem rather useless.. untill you consider that it allows the tec to place 2 novaliths per planet, instead of one. The advent can already place 2 love cannons, so not very helpful to them. In general though, give to the player with the most boarder worlds.
Structure pact: The tec have alot of hull, so this clearly benifits them the most. That sounds familiar... huh.
Armerment pact: This benifits both other races preety equally. Give this to whoever has the largest fleet.
In general, the Vasari pacts benifit the TEC, so, once again, if you have to choose where to send your diplo cruisers, make friends with a tec person.
I hope this helps you get some ideas on tatical pact forming. These things can seriously tip the scales, and the bonuses of having diplo cruisers at allied planets to form these pacts makes it even better. However, dont go for these pacts if you are not in a econ spot, or you will prolly get rushed and destroyed before these pacts take effect... and all the missle pacts in the world dont do anything if you dont have any ships.
Pacts and diplo cruisers are great, and by themselves make diplomacy a great and worthwhile addition to the multiplayer game. I hope to see you all in the diplomacy ICO lobby soon!
(any thoughts? did i miss anything?)