I've looked at USB scopes, and I actually borrowed one for a few days a couple of years ago, but I didn't really like it well enough to buy one.

My biggest complaint is that my computer is busy enough already. When I'm working, I've often got schematics and PCB layouts open on screen, maybe a data sheet or 2, Microcode Studio, and who knows what else.
My computer is BUSY and there just ain't room on screen for it to play 'scope too...

If I had a spare laptop laying around, that might be different.

Besides, I like my scope to be "self contained" so it's easily portable.
It's a neat concept, and I'm sure a lot of folks love 'em, but I think they just don't suit my work style.

steve