Thanks for all of the replies so far.
I fully realize that this is something I don't need, and I won't buy it until I feel that I have the money to spend on it (which I'm hoping will be some time this year). Here are some uses I have for it:
* A second computer for the house. I was planning on building one for my basement, because I'd like to have one next to my workbench there. With the laptop, I could keep it there normally, and when I want to use it elsewhere, just disconnect it and take it with me. I have CAT-5 through the house, so I can run a cable through the floor to where I'd connect the laptop to. Also, if I want to use a PC in another room, I can take the laptop there and connect it to my DSL. I have CAT-5 jacks in all 3 bedrooms and the living room.
* Portable & wireless internet - when I'm on a long trip or vacation, it would come in very handy. In a hotel, I could connect it to the room's broadband system. This is something I need to look into more, though, because I don't know much about how Wi-Fi works, how much it costs, where I can actually do it, etc..
* Gaming on my TV. I have thought about connecting my PC to my TV to play Doom 3 there, but this is of course impractical as they are in different rooms. With the laptop, I can use the S-video TV-out capability, or possibly even the DVI-out (since my TV has a DVI input, although I'm not certain this will work, as the manual says it's not intended for PCs, but I have heard others say that it will work anyway). This is why I want the power of the XPS: it will run Doom 3, and probably Quake IV, very well. In fact, probably better than my PC (Athlon XP 3200+, 1 GB 512M x 2 dual channel DDR400, nForce 2 Ultra chipset, GeForce 6600
GT).
I will definitely get at least 1 GB of RAM. Only thing that sucks about that choice, well it's both good and bad, is that the 1 GB comes as two modules, and the board has only two slots. Of course this is necessary for dual-channel, but it also means that if I decide to upgrade to 2 GB in the future, I have to get rid of the two 512M modules. And the price difference between 1 GB and 2 GB is... $550. Ouch. It seems that it may be better to get just one 1 GB module now, but that's not listed as an option. I wouldn't have DDR, but I think it would still be sufficient for my purposes, and upgrading to 2 GB later wouldn't require me to sacrifice any modules that I already have. I wonder how comparable the overall performace of the machine would be of 1 GB w/ dual channel and two 512 M modules or 1 GB of non dual-channel with a single 1 GB module?