Since we first heard about it a month ago, Midnight Inbox has been improving by leaps and bounds. One only needs to check Midnight Beep Softwork's development blog to get updated on all the changes and improvements (far too many to thoroughly list here), but put simply: a lot of performance and stability improvements have been made and the UI has received a significant update. Midnight Beep has been keeping a very open ear to user feedback, and they have a lot of cool features coming down the pipeline, such as: iCal syncing, printing of hipster PDA cards, archiving, live filters and search, support for Quicksilver, Automator and AppleScript and of course - language localizations.
For beating some heavier hitters to market with what is quite possibly the first true GTD app, Midnight Inbox certainly doesn't look too shabby, and neither does its $35 price tag. Check out Midnight Beep Softwork's site for more details and to take a demo for a spin.