I've had mine for around a week and really like it.
Physically comparing it to my co-worker's Eee PC 900, the Wind is about 1" wider and 1/2" deeper, and besides the slightly larger screen the Wind has a larger keyboard with larger keys. I have not actually used any other netbook, so this ends my comparison with those.
I do have experience with normal notebooks/laptops, so of course the immediate comparisons would be that it is of course smaller, gets better battery life (mine came wit 6 cell), is lighter and is less performance. When I say "less performance," the slowest notebook I've owned had a 1.3GHz Banias (Pentium M) chip, which is of course faster than a single core Atom. My current two notebooks are a 1.6GHz Dothan (newer Pentium M) with 2GB RAM running XP, and a 2.0GHz Core 2 Duo with 4GB RAM running Vista 64. The Wind came with XP Home.
I haven't done anything intensive on the Wind yet, just some web browsing and typing up several paragraphs. Basically I used it for about 5-6 hours, until the battery warning came up.
I am happy with my purchase. My wife tried it out and was unhappy though, until I ordered her one as well. 😱
Again, I don't have any real experience with other netbooks for comparison, though some minor comparisons can be drawn from what I read elsewhere.
Top competitiors are of course any 8.9" and 10" netbook.
The Asus N10J uses a similar screen, but the notebook is physically a lot larger and is 0.9 pounds heavier. The only benefits are the discrete NVIDIA GPU and the extra GB RAM.
The Asus Eee PC 1000HA is pretty darn similar, except for weighing a bit more (maybe 3/4 pound?).
The 8.9" screen units with hard drives are pretty similar in weight and are a bit smaller in physical size. This includes the Eee PC 900/901/904, Acer Aspire One (which was my top choice until I found out more about the Wind) and maybe a few others.
All of the netbooks I looked at have 6 cell batteries, because I do want the longer unplugged life, plus hard drives and 1GB RAM. The 10" ones are usually around $500 except for the N10J which can be as high as $800. The 8.9" ones are usually around $400. Anything cheaper usually has half the RAM and/or a small SSD.