I had the opportunity to install FreeBSD 6.2 on a brand, spanking, new Dell 2950 the other day. It slid right on with absolutely no problems.
The Dell 2950 has the Perc 5/i RAID controller and was preconfigured in a RAID 5 by Dell with 4 x 73GB SAS 15K drives.
FreeBSD installed with no hassles at all. No messing around with drivers for RAID cards, network cards, etc. Love it.
One weirdness: When did Dell stop including PS2 keyboard ports on the back of their servers? Now the KVM switch is officially useless and we had to run around the data centre trying to beg, borrow, or steal a USB keyboard.