Try a clean install. As always, this is the preferred method for upgrading. (This is because there can be user-installed software that had explicit dependencies on the older environment.)
And just FYI, to do a clean install with only one download of Lion you need to burn a disk or create a USB stick before you install it because it deletes the installer.
See http://lifehacker.com/5823096/how-to-burn-your-own-lion-inst...
I am happy to know, it works fine for most people. May I try to make a clean install. But if it doesn't work better, I'll have to downgrade.
I don't think I have a "strange" configuration. I don't remind playing with the kernel or using very specific configuration.