The GMail application has also been subtly improved with little checkmarks that allow you to select multiple items for tasks like deleting spam. Unfortunately, GMail is actually a bit slower now than it was before the update. In fact despite Cupcake's improvments, my G1 phone is still relatively slow at times. It's not overwhelmingly slow but does slow down nevertheless.
Another disappointment? Twidget, the little widget for displaying Twitter updates. I really like this little widget at first but after about 24 hours it started crashing repeatedly and I had to uninstall it. This is a shame, I hope it gets fixed soon because it was a nice little app.