I used to run windowblinds comfortably on a p2 233, 160mb ram with a 32mb pci graphics card, with no slowdown worth worrying about. As for resource usage, I find it negligible, especially given the continued memory optimisations which the Stardock people have undertaken. Googling around results in similar discussions elsewhere, often by people much more qualified to speak about it than me.
If it's that big a deal it's a two click process to unload it for when you're working on something REALLY resource-heavy, but I'm finding that through improvements at their end in terms of memory usage I need to do that much less these days.
And in response to people "pimping their desktops", the reason I do it is because I spend a significant period of time working at my computer. I'd much prefer something that is pleasant to something which is ugly, given how long I spend looking at it each day.
That said, if the computer you want to run it on falls much beneath p2 233ish, it might be a better idea investigating some of the shell replacements. Another factor which I forgot to mention is that windowblinds can take advantage of hardware acceleration, if the machine can handle it, which probably helps a heap. Given that I've never used it on a machine without hardware acceleration, it may well suck big time without it, I don't really know.
