Why are apps logging me in as someone else?
This has happen to me with some apps...

Did you lost your IMEI?

I mean, maybe in the process of rooting, sim-unlocking, rom updating your phone, etc... you did something wrong and "lost your IMEI". It seems having an IMEI of 004999010640000 indicates so. At least this happened to me with my Galaxy S (I9000)

Some apps seem to uniquely identify a user by IMEI. If you have this 004999010640000 IMEI you are now part of a club of hundreds with that exact same wrong IMEI. So someone who also "lost his IMEI" might have registered to those apps before. This happened to me with OpenFeint for example.

To check your IMEI go to Settings > About phone > Status