We've had a couple reports of the latest Gmail update no longer appearing in the Market, and now we have a reason why. It seems that users who were still using a 2.2 version of Gmail and updated to the latest version had some stability issues. Users who updated from a 2.3.x version are unaffected.
If you are experiencing bugs or crashes since updating, Google recommends you remove the update by by going in to Settings > Applications > Manage applications > Gmail > Uninstall updates. A fix is in the works, and we expect an even updated-ier version soon. [Google Mobile help forums]