Go check the Android Market now for the next version of SMS Popup - it includes a bunch of bug fixes and a few new (very requested) features!
As a side note, if anyone would like to help me translate the app for the following countries, please send me an email (adam at everythingandroid dot net):
Austria, Czech Republic, Germany, Netherlands, Poland
(of course if you would like to translate for other languages let me know as well).

SMS Popup v0.9.4
- Tons of bug fixes, mostly to do with the WakeLock code which was causing the app to "force close" intermittently. Hopefully this fixes the majority of major bugs but time will tell.
- Basic MMS support - this was more difficult to implement than I thought. The app should now detect MMS's and trigger a regular (non-popup) notification (it should be almost identical to the system one). It will not turn on the screen or show a nice popup yet - I will try and add this in the next version.
- Configurable vibrate patterns - choose from a list of pre-set vibrate patterns or create your own :)
- Fixed the landscape layout so it fits correctly when the contact has a photo