I have some left hand knowledge, not necessarily first hand.
Most HP computers come in a variety of letter variations. "D" is their standard line. If you're not running any games on it, it's a basic general use box, good for showing movies and stuff. "B" is their business line, with more streamlined functionality and powerful processors, but less emphasis on media (speakers aren't as fancy, that sort of thing.) "E" is the elite line, which is the best of the D and B lines rolled into one unit. "W" is their workstation line, which are the most powerful (and most expensive) machines - and then there is the Z series, which is a class in its own sexy self.
HP, like any other manufacture, can have the occasional lemon. But my experience with HP has beaten the pants off any other PC or laptop I've had. You just have to know what to expect out of them. For laptops, absolutely get the 3 year warranty. You'll need it for the power supply after a year at the very least.
For desktops, if you can do your own repairs and upgrades, there's no point . . . I treat HP boxes as a starter kit, and just add on and upgrade as necessary. My current box is approaching two years old. I paid $350 for a refurbished unit, dropped in an nVidia Geforce 9600, a 650 watt power supply, and doubled the RAM. It's been a good box - I haven't even had a fan wear out yet.
Looking over the specs for that, it's actually a really good base for a system. You're starting with a terabyte of storage, maxed out RAM, and a Core i7 on the very latest OS. Radeon HD 4650 is a decent card, and that can be upgraded easily if you ever feel like it.
Edited, Dec 11th 2009 4:30pm by catwho