@slender
Don't worry. I don't need to know how to backup and flash my device from now, internet is always in access for these problems. and next time when an amateur like me asks a question, if you know how to help, help her/him, if not, please just don't try to make her/him disappointed! Thanks.
Famous last words of anonymous user n+1 who thought that app in testing/devel repository or in page xyz is just harmless thing.
I was just trying to help you with possible headaches that could be around corner.
ps.
By referring that you have always acces to internet i hope that you mean mostly google (power search here).
slender is right, made some regular backup beacuse if your N900 won't boot anymore after an appz installation, you may loose your data, contacts, emails or whatever file you used to have
