My boxwave stylus arrived today (that was fast, I used the cheapest shipping and my order from Sunday 6/6 arrived Thursday 6/10). The tip of it is kind of like an air-filled rubber ball (I got that description from another reviewer, but it really fits well). Very sturdy, easily glides across the iPad screen, and I have no fear of the tip breaking off. The thickness is fine too; it's a bit thicker than one of those $.10 pens but not thicker than a normal nice pen.
I tested it with a couple of apps, the first of which was Penultimate. Penultimate is very responsive to stylus writing (as to be expected since it was designed specifically for stylus support). You don't have to press hard to write, and the app does a great job of following your writing. Penultimate also has a nice "wrist guard" feature so you can have your wrist on the iPad screen while you write. With the other programs I've tested you have to be careful how you hover over the screen or else you will start drawing with your wrist.
Next I tried SketchBook Pro. Again the experience was great, although without wrist guard you have to be careful how you hold the stylus. For precise brush strokes you can zoom in on the image. This still isn't a replacement for good old pen-and-paper drawing but it is a lot better than trying to draw with your finger tip.
Last I tried Paper Desk. I can see why Penultimate is so popular... stylus support in Paper Desk is not so great. You can make crude drawings but writing is nearly impossible.
Overall I'm happy with the boxwave stylus. I haven't tried any other iPad stylus so I have nothing to compare it to. As a side note I'm not sure why they included a little keychain loop attachment at the top of the stylus as it clanks like crazy when you're writing, but it was easy to remove. Boxwave is also releasing a "styra" version of their stylus that will double as a ballpoint pen, but I was afraid to order that one thinking that someone unfamiliar with the iPad may try to use the pen side for more precise writing