I picked up a black one last night and put it through its paces a few minutes with R-Type Delta. I think the review from IGN is dead on.
The first thing I thought about when I took it out of its package was how well it was built for being so small. It has a very nice feel holding it in your hands and I especially like the rubberized grip on the back of the controller. The buttons are also nice and very responsive and the backlighting is a really cool feature. I also had no problem with the way they chose to put the shoulder buttons side to side (to keep the slim profile) instead of back to front.
There are a few negatives. My main gripe is that D-pad. It has a very low profile, almost to the point that it feels as if the d-pad is sticking if you are used to the give of other controllers. It is like you have to press down kind of hard to get the response you want and doing so makes it seem like the face of the d-pad is actually inside the controller. It just makes for a sluggish and sloppy feel for it all.
While I like the stiffness of the analog sticks (a little more stiff than the Dual Shock and a lot more than the cordless Logitech controller), I thought that they were a little small and too close together. I like to use the ball of my thumb instead of the tip for analog control and doing so causes my thumbs to constantly wrestle with eachother for space. If you use the tips of your thumbs though, this shouldn't be a problem. I consider myself to have normal sized hands (no problems with the old NES bone controller) but I wanted a little more analog stick to hold on to. Just like someone else in this thread mentioned, I also found that you had to press pretty hard to get the analog sticks to click. And for some reason the left one was harder to click than the right.
Overall, I'm pretty happy, especially considering the value. I plan to pick up another one so my daughter can use if for Katamari. If I had to rate it, I would give it a 7/10 due to the d-pad and analog sticks but for the value its a 9/10 considering you don't use the D-pad much.