Having swung over to a Nikon D90 from Canon film SLRs after a long interlude with high end compacts, I knew the essential accessory was a bounce flash. My Canon Speedlite EX series flash is big, zoom head, 4 batteries. It hardly ever left the house. I decided I wanted something smaller and not a drag to carry around with my D90 and got the SB-400. I've had mine for 3 months now.
Practicality: It is small and light, I take it everywhere with my camera, even on holiday, on days out, etc etc (so it actually gets used unlike my Canon used to). I'm glad I did not spend more money on a larger Nikon flash unit.
Colour and exposure: Colours are great, no blown highlights, exposure generally good, sometimes need to up the flash compensation.
Coverage: The surprising thing about this flash is its even coverage when used at the wide end of a 16-85mm zoom. At 16mm (24mm equivlent) this flash lights up a room briliantly and my old canon speedlite struggled at 28mm which the zoom head supported (then "full-frame" of couse). This means the normal wide end (18mm) of most kit lenses will be easily handled.
Features: There are no advanced controls on this flash, just on/ff and lock lever (neat - again one up on Canon) but it can be controlled from in camera buttons and menus as much as the built in flash. This means on a D90: max 1/200th sec synch speed and gives you front/rear curtain, slow synch, auto fill in, manual, auto red eye, flash exp compensation. Repeating (strobe) and commander mode are not supported. What else do you need? Wireless remote if your camera body supports it? Well...
Lastly for those that want swivel too, you can buy a hotshoe cord for a bit over £20, so you can point it in direction you care. So that makes it a bounce, swivel, off camera flash for £120... Oh - the 2 AA batteries last a long time...
This flash is a no brainer for most situations, so use the money you save on its bigger expensive brothers and buy another lens instead. If you can afford and want the more expensive solutions, get one of these anyway for portability. Go buy. I cannot comment on the seller, bought via another supplier. Look for prices under £100, or near to £95 to compete with the high street or retail park stores.