I am usually one of the first few people to upgrade my Ubuntu installation every time Canonical releases a new build of Ubuntu. However, I had noticed a few users having problems with their upgrades and decided to "wait and see".
There are now quite a few users reporting that Intel Graphic owners have problems with the KMS (Kernel Mode Switch) with the new kernels. I strongly suggest owners to wait until this problem is resolved and stick with Karmic Koala until then. You can find out more about this issue at the ubuntuforums.org site with a Google query here.
I've read some websites saying that there is a quick fix to the problem where the kernel switches off KMS on known problematic graphic chipsets. Though this makes it easier to move from Karmic to Lucid, I'm personally going to wait until the problem is fixed (fixed with functionality, not fixed by switching the function off on problem machines). You can read about this workaround here.