I've got to mostly agree with Doc on this one since there are MANY reasons for choosing the perfect computer for someone. In some cases, buying an elcheapo and upgrading the memory is worth it if they don't need graphics other than email and web. For a gamer, the more expensive machines are probably going to be what they want.
That all being said, I typically stay away from Dell machines since I've had bad experiences with them in Enterprise environments (although I'm fine with their servers). I was using a full blown 17 inch Toshiba (a gamer) for personal use and liked it, but it got way too hot and was too heavy to just carry around - I gave that to my wife who was mostly a desktop person. At the moment, I'm personally using a Macbook Pro 15 inch for personal use (19 second startup, 5hrs of battery life and a unix/linux environment - can't beat it). For biz use, I actually just made the jump into an HP 3G enabled netbook. While it's taking some getting use to due to the size, I'm pleasently happy with it since I can carry it to a customer site (it barely ads weight to my bag and they don't see an obvious shape of a laptop being carried around). The 3G comes in handy when I need to get something quick and not need to worry about getting the wireless password, etc.
When someone asks "what type of computer should I buy", I really sit down and interview them to see what their current and future uses are going to be. If you customize their computer to their needs, it'll usually fit their budget better and they'll be happier. Oh, and if it's a desktop, I'll typically offer to custom build what they want.