Thanks for the info.
My iMac still runs Tiger because I run Ubuntu almost exclusively anyway. However, I started thinking about getting an iPad, and it seems that you either need a Windows computer (which I do not have) or Snow Leopard to activate/sync an iPad.
I could just pay 129 euros for a Snow Leopard license, but that would just feel like a markup on top of the price of an iPad for no reason.
That's why I started thinking about getting a Macbook Pro or Air.
I would probably not run Ubuntu on a Macbook Pro or Air. On a desktop, I very much prefer Ubuntu over OS X. However, on a laptop, the advantages of OS X (battery life, hardware support etc) are much more important than on a desktop. Maybe I would use some virtualisation to run specific linux programmes.
Based on the above, I guess I don't care that much that I would not upgrade to Snow Leopard on my iMac...
Another (minimalistic) option is to activate the iPad in the store and not sync it to a computer...
Oh well. No iPad for me. I'll have another look when there are new Macbook Airs, and when Lion comes out.