I just bought a base 21.5" and love it! Absolutely love it!
Except when it locks up.
Which is a lot.
Like every day, multiple times for the 11 days I've had it. Force Quit does not work, powering off is the only option.
The last several days it seems like iTunes is the culprit but a complete uninstall and then a reinstall did not correct it.
Google searches show that's it's happening all over but not just with iTunes.
And not just with Lion -- I have the most recent version of Snow Leopard myself.
Google searches also reveal that this has been a recurring problem through time with different model iMacs and that Apple will fix it.
So.............I say go for it!