Lion Crashing

I've got a MacbookPro and I have recently installed Lion OS.

Since then the computer keeps crashing randomly at least 3 or 4 times a day.

Does anyone have an idea why and what could be done about it?

Lots of folks are having the same problem. Usually it is caused by incompatible (i.e. outdated) software, such as login items or extensions that weren't disabled by the OS X installer when upgrading. Disable all login items and any utilities that modify the OS, or which work deep within the OS, and see if the problem persists.

If you can't locate the offending software, your only recourse is to do a clean re-installation of Lion:

HOW TO: Do a Clean Install of OS X Lion
Should you do a 'clean install' of Lion? ( - Software )
OS X Lion: How to Do a Clean Install

In my humble opinion, Apple made a huge mistake when they removed the "Archive and Install" option in the OS X installer.