It's very fast (native app), it supports practically every type of mail account ever, everything can be stored locally (great for offline batch processing of emails), and there are keyboard shortcuts for everything. It takes a bit of customization to get a layout that works nicely for my workflow (I use the classic layout).
There are a bunch of other 'efficient' mail apps, but if you just need basic features and don't go for some exotic or trendy workflow, Mail works fine.
I don't upgrade to the latest OS for at least a few weeks, though, because if something like this is systemic, it will be fixed in the .1 or .2 release.
Also, always keep at least one local backup (I have Time Machine for that), and at least one remote backup.