Google has pulled yesterdays Gmail update from the market due to stability issues from users updating from Gmail 2.2 to 2.3.4 (the new version). Anybody that updated from Gmail 2.3.x is not affected by this bug.
A work around has been found for those users currently experiencing issues:
Home>Settings>Applications>Manage Applications> Gmail>Uninstall Updates
A new Gmail update is being revised at this time, now that they’ve learned of the bug, and is expected soon. Definitely says something for responsiveness.
Source: Android Central via Google Mobile Help Forums
