The first thing most people notice is the small nine inch screen. At just 1024x600 it is a little cramped, but the display is very sharp and small fonts render well. I suggest running Firefox in full screen (kiosk) mode to maximize your display area. If you're looking for the F11 key, it's available, but hiding if you have a newer BIOS. fn z and x are F11 and 12 respectively. This makes switching in and out of full screen mode easier.
Everyone I've shown the netbook to wants to know about the keyboard. It is smaller than a normal laptop keyboard, but not as bad as the Asus eee 2G. I find that my right hand feels a little cramped and the number placement isn't quite right, but I can still touch type on it with my fat fingers. The hardest thing to adapt to is the location of some of the punctuation, especially the tilde, pipe, and backslash. The grave and tilde have moved to fn q and w respectively and the pipe and backslash moved to the right of the P with the punctuation from right of the zero.
Solid State Disks rock. The Mini 9 uses a standard mini PCIe solid state disk. While it's not terribly fast, it is low power and at least as fast as I think it needs to be. My mini has an 8GB disk, but Dell offers reasonable prices on larger ones if you need the upgrade. Alternately you can upgrade through crucial or the like for cheap. I found a 32GB SSD for just $75. I'll just keep my documents on an SD card or USB Thumb drive for now.
Performance is acceptable. The 1.6Ghz Atom processor is capable of streaming Hulu.com, playing mp3s, and playing a DIVX encoded movie off SD or SSD so I'm happy enough for now. Firefox performs well, even when streaming You Tube. I did bump the RAM to 2GB DDR2 PC-6400 for $27 (+shipping). Dell's price for the same upgrade is $75.
I've been traveling with an HP tablet PC for about 4 years now, so I have already adapted to life without the optical drive, but once in a while I need to burn a disk for someone. For that purpose I picked up an I/O Magic CD/DVD Burninator. That isn't it's real name, but I plan to etch an image of Trogdor on the cover, so it's fitting. I haven't put it through the ringer yet, but it's worked for a couple Ubuntu installs and burning an audio CD.
The battery is rated at 14.8V at 32 Watt hours, yielding just over 4 hours of run time. The included wall-wart style power supply outputs 19V at up to 1.5A and makes quick work of charging the battery, giving an 80% charge in under an hour. I might have to google or experiment with powering it off the car's power, but even if it runs, I'm sure it won't charge the battery. Someday I'd like to have a machine that I can use in the car without needing an invertor.
See my Mini 9 set on Flickr for more info.