on the same note, I was playing a single player game and noticed one of my AI enemies doing something pretty crafty. My hangars were consistantly killing his scouts, so after probably the 3rd scout that was killed, he started sending flak frigates to scout my planets. It may have been a more expensive option, but his "scouting" flaks survived and he weakened several of my planets defenses by destroying their fighter squadrons. It was some nice adaptability that I wasnt expecting from the AI, kudos to the programmers.
the one problem with using anything other than a scout for scouting is that you have to do it all manually as other units dont have the scout ability. also, other ships are quite a bit slower so it will take a lot longer for you to cover the same amount of planets your normal scouts would.
I play mostly against AI or LAN opponents, since my internet connection blows...Hangars do the job nicely. Scouts rarely get past my edge planets, but then I am a fanatic about building hangar defenses. First it discourages the AI. Second, once you kill the seige craft, pirates are a minor annoyance. Third, they don't have a range. Fourth, they make a nice 'non-fleet cap' addition to my fleet if I ever have to fall back. Add in a repair platform and, unless you get blind-sided by an enemy armada, you'll always have time to muster a fleet defense. 12-14 bombers take out an HC every other pass.Beam/Cannon defenses never seem to cut it for myself.
i do love hangers as well, but i usually only stick with 1-2 per planet to discourage scouts, unless i have a ton of money to burn (unfortunately this is not a problem i often face). i do find turrets useful at times, since you can have 4 of them for every hanger (6 in advent's case) just giving up 1 hanger can give you 4 turrets, or 2 turrets and a repair generator that you can use to cover the hanger's themselves, you'd be suprised at how much more hesitent people are about taking out hangers when they have a nice battery of 4 turrets surrounding them. wont do a thing against larger fleets but aginst small raids it can be really nice.