Overall the program is much better than AppleMail, in it's operation. Two somewhat minor bugs I've noticed using Gyazmail the last six or so months:
1. When selecting items in a folder, the selected items scrolled in a window get fuzzy and tend to almost become unreadable.
2. This program lacks an export feature to export messages to text files. Because of the way other programs work, an an example Micorsoft Entourage, you may not be able to drag and drop messages or folders properly to those programs (or export them in any other way). This is less a fault in GyazMail and more a problem in those text based programs though.