Here at TiPb, we've all had bugs with the leaked 2.0 update and, like the rest of the interw00ts, we're also not getting Mobile Me working reliably since it went live yesterday. Thankfully, Apple has fessed up and admitted that the transition from .Mac has "taken longer than expected" (per Engadget).
The Mobile Me desktop login just worked for me for the first time just now, this morning. I'm successfully pushing data out, but I'm not about to start depending on it for real work. Is it working for you?