I don't know if it is a case of "the grass is always a little greener" but, I have a 360, I've had it for almost two years now, and it is the most used console in the house. I enjoy the dozen or so games I have for it, though mostly I'm playing Fallout 3 and a few Xbox Live Arcade games I bought. (Portal, Geometry Wars, Puzzle Quest)
And yet, I wonder if I could have enjoyed the PS3 more? I know it's more powerful. I know that the games I play now (Fallout 3, Oblivion, Bioshock) are all available on the PS3, and games I would like to play (Little Big Planet, Final Fantasy XIV, Siren 3? I think) are either exclusive to the PS3 or are getting there first. I also wouldn't be living with the fear that I'm going to get a red ring again on the 360.
Mimi, my advice would be to find a friend with whom you can trade systems and games for a few weeks. If there's game rental place in Tokyo, then trade systems with a friend, rent a few games for the 360 and see how you feel. After a few weeks, you may know whether or not you need to change your system. Hope this helps.