Here's the approximate numbers I think of. I think they're fairly similar to what you'll here elsewhere:

Heavy, unpleasant backpacking - 18+ lbs
Lightweight backpacking - 10-18 lbs
Ultralight - 5-10 lbs
SUL - 3-5 lbs
XUL - <3 lbs (not recommended in any way)

These are all just arbitrary terms. I used to think it would make a big difference if I "went" SUL, cutting out another pound of weight. Then I realized that if I was carrying enough food and water, the extra pound would end up being only a 5% weight decrease for a lot of sacrifices.