@larryxTo quote myself regarding the "ICO-warning message" again...
@ EVERYONE - IMPORTANT
I have seen that message from IronClad "...Most people will not be able to join your game...." everytime I've hosted since the first 2 or three games I hosted (and I haven't changed anything on my end). The games I host are still able to be joined by EVERYONE and everything works like a charm! What this means is, that IronClad have intruduced a "connection checking" method on their end which takes into consideration WAN ping, IDENT (maybe), open ports, etc. If you fail even one of those, their message pops up. While ping and ident are an easy way to see if a host is online or not, they're not required at all for the actual "connection process".
To re-cap, seeing that message from IronClad doesn't at all mean that it won't work. Ever since they setup their "connection-testing" I've been getting that message as well. I don't allow WAN ping or IDENT so I'm assuming that's why my setup "fails". In any case, I am able (and have many times now) to HOST without any issues whatsoever!
the Monk
@KreysonWith regard to being able to Host in all other games. Even IF all the "other" games you reference had used the SAME ports that Sins uses they would have used them in a different way. Sins is peer-to-peer (unlike most other games) and due to its ability to "migrate" from a dropped host to another (correctly configured) host in-play requires TCP connections to not be broken by NAT. When you're not using a "centralized" game-server/dedicated server (and this was done for obvious reasons), the community will need to LEARN a few things.
It's not the game's or game designers fault most people today are using technology (routers, firewalls) which they barely understand. I'm guessing you have to understand and follow the "rules of the road" when you're driving your car? What's different here? Learn, and follow the "rules of internet-traffic" and like many of us you'll be able to say: "I have never, and never will have a problem hosting/playing any game ever"

Why? Because I understand and follow the rules of the road. You can too.
Having said that, there is plenty of information on these forums alone to give you a nice understanding of WHAT needs to be done to have problematic-free gaming. The HOW you may need some help with. If you need help with the HOW, I'm usually available on my TS Server to talk people through it. Contact me via xfire (my information is in the sticky at the top) to set up a time to get on my TS with me.
the Monk