If you have an external drive connected via Firewire you could try installing a pristine version of Lion on a partition and then run your Mac from the external.
If if it works well, then I would suspect some sort of conflict with one of the apps or drivers installed on your Mac.
FWIW, installing a major OS upgrade on a Mac that is running fine is always risky, particularly the initial release... I tend to wait until at least version 10.X.3 or even later depending on user reports about bugs.
One of the advantages to having an external drive with a bootable clone of your Mac's drive is that you can install a new OS on either the internal or external drive and see how well it works for you. In either scenario it is very easy to switch back to the working OS if you run into problems.
I never do a major upgrade without having a recent clone available in case of trouble. In fact, I run SuperDuper! before any software update Just In Case... And I'm the kind of Mac user who makes sure that all apps are compatible with the new OS before upgrading.
I recently purchased a 13" MBP that I thought would come with Snow Leopard but instead has Lion. (Amazon's products description page was inaccurate and it was corrected a couple of days after I purchased the MBP.)
It's the first time that I have not used Migration Assistant to transfer data from another Mac. I figured that since Lion is markedly different from SL that I would start with a fresh installation and only install the apps that I need on the MBP. So far the MBP is running like a champ and I don't have all the left-over dross of myriad apps that I have collected on my iMac.
If you had done a major OS upgrade on a Windows PC you could also experience problems after a major OS upgrade. It's not a Mac vs. Windows issue... Unless you are running a stock Mac configuration with no third-party apps, etc. it is highly likely that something will be broken after an upgrade. Drivers are a common source of woes after an upgrade. Since most of us customize the heck out of our Macs, it only makes sense to exercise caution when doing a major OS upgrade.
Unfortunately, the move to easy downloading of OS upgrades via the App Store makes it very easy for people to upgrade before a new OS is really ready for Prime Time. I prefer to let others be the early-adopters and discover the bugs before I upgrade.