Can anyone point me to reference material or overall strategy or example code for including a time limit or expiration date (or timebomb) in a "free trial" Maemo5 app?

There are many approach, the simplest one:
1. create a file with a timestamp of the installation program
2. everytime the program run, read the file and check the current date
3.if its more than 30 days then put message and exit.