Yes I have similar problems too. When I get a message on the "grey display" (which you drag down) that there is updates in the Market, and I try open this message from there -> the whole Market App gets stuck.
It askes for a password (for my Youtube acct, I use Market thru Google-acct) but I doesn't accept the valid password (I've checked the passwords thru PC, also my Android Market works from there).
Last time I had this problem a couple of weeks ago it sorted out in two (?) days - suddenly the Market App just asked which acct I want to use and clicked Google, gave the password and it was over... Now I had forgotten the whole thing and did the same on the grey display again with known results: "You gave wrong password or your account has changed". And the right password won't do.
Well now I'm waiting for a couple of days if it would sort out by itself as the last time. Is there a bug on the new Market app? It certainly started with it.
I have a Samsung Galaxy S II (GT-I9100).