I just bought the LowePro Slingshot 100 today, and it appears to be a great bag. It's almost as comfortable as my Tamrac backpack, and I think the slight loss in the comfort factor will be offset by the ease of getting to my camera.
It was tough deciding between the 100 and 200, and I may still go back and swap it for the bigger one. The 100 holds my D70 along with my 18-70 and 55-200 lenses (one attached to the camera body). But if I upgrade to the 70-300 VR, I'm concerned it won't fit. Thing is, I'm a smallish person (5'2" if I stand up really tall

), so I want the most compact bag that will safely hold all the stuff I want to carry. I ordered a Crumpler $4M Home (
http://www.crumplerbags.com/Cart/index.php?catId=22)a few weeks ago, and although I loved the look of it, it was just too small for my needs, and not at all comfortable to carry. I got the blue one, and I so wanted to like it because it looked so much better than any other camera bag I've seen (how ridiculous is that?), but ultimately I decided the cool factor was not worth the chiropractor bills I'd incur if I carried it (or worse, the $5M Home) around on vacation. A vest would no doubt be the most practical option, but I just don't think I can go that far!