i'd go with Olympus.
i do quite a bit of traveling and have realised that weight really makes a difference. Olympus, because of the Four Thirds technology, can afford to make the lenses lighter. this saves a lot of weight.

most people go for Nikon/Canon because there range of lenses and flash guns are wider. more shops also sell them. if you aren't investing in new lenses anytime soon, then Olympus twin lens kit would be fine.

i use the E-500, so i wouldn't know much about the IS. haven't had the chance to try it out yet. the Supersonic Wave Filter helps out a lot though. especially if you change lenses often and in the outdoors.

but with whichever camera you get, have fun with it