The main focus of this new version was localization. It now ships with translations for 8 languages (4 of them basically complete, thanks translators!), and also supports displaying the amounts in currencies other than USD including EUR and GBP. It also sports a few of the typical bug fixes / usability improvements you would expect in a new release.
Another feature new to 0.4 is a setup.py, which allows Linux users to install it easily by running "sudo python setup.py install" in the folder, and wxBanker will install itself including a shortcut in Applications -> Office in Gnome, and store your data in ~/.wxbanker. If you are upgrading from a previous release, I recommend moving your bank.db file to ~/.wxbanker/bank.db for the easiest transition, which will also future-proof you from needing to shuffle it around in the future!
I also thought I'd highlight the launchpad integration I added awhile ago in 0.3, since I saw a recent planet post regarding Inkscape doing something similar. In the Help menu I've added convenient links to view and ask questions, and report bugs:

If you have been looking to start taking control of your finances, give wxBanker a try: https://launchpad.net/wxbanker/trunk/0.4 (or 'bzr co lp:wxbanker -r 86' for the seasoned). If you find problems or have ideas, please let me know via launchpad bugs/blueprints, blog comments, or email; if you know another language, help translate by following the Translations link on Launchpad! And remember, when you use wxBanker to count your pennies, the dollars will follow!