i would agree with most of the people that buying one off the shelf would be a good deal if your not keen on building your own.
For me atleast like scubafreak said depending it may be better to build it if you know what your doing and are looking for a higher end machine. For example the desktop is just built for graphic editting rig (PS, Illistrator, etc) cost me about 1300 for everything for the box and this includes AMD xp 3200+ 400 FSB (one of the fastest Processors on the market, sorry dont care for intel), 10K rpm SATA drives, 1GB of 2-2-2 CAS memory(lower the cas number the more efficient the memory), Sonys new Superdrive, and a matrox Parphelia video card, just for a couple items on the box, but its a fully loaded rig.
In stark contrast i priced out the same specs out with several major makers and was shocked at what this would cost to get built by them. First off was Falcon Northwest and it came to $3100, a couple of local makers at around 2800, and alienware at 3700 which blew me away as that was really high. so as a resulti built the box my self and havent had any problems with any of the components
(BTW, Dell, gateway, and Compaq/HP werent on the list because they couldnt provide a system with some of the essential(proc, Ram, and Video card) items i wanted in the system)
As for the restore disks they are worth anything as its a generic image that is loaded to all the machines, if you really want a back up copy of your base install go buy a copy of ghost and use it for doing backups( but make sure you have a seperate partition as you cant put a ghost image on the same partition as the desitnation of the ghost image.
FWIW
Tooth