When I'm designing, there are times that I have to decide between pretty (large images, full-page backgrounds, animations) and quick.
I read in a book long ago that you should keep your homepage under 50kb. What do you use as an upper limit?
I don't think there are any strict limits, it depends on each client and each design. My upper-limit is 'as small as it possibly can be'
Once you've optimized an image, if it is still very big it would be time to accept its size (and the higher hosting charges it could potentially bring), or redesign and use a smaller/less complex image.