Upgrades:
* Memory
* Hard drive
* DVD player
* Cd-burner
* Network card
* Modem
* Video capturing
* video card
* Zip drives
* motherboard/cpu upgrades
 
Most people walk into a retail store (cough! best bye.. or ahem.. computer usa) and don't have a clue what they want or need.  When they ask for help, they aren't usually so helpful either.  Even if they were helpful, all the computers at a retail store are pre-built by manufacturers with components you may or may not need.  If you were to customize a computer at a retail store, you'd have to pay for parts you don't even want, then pay $50 & up just for labor, plus the parts themselves, and that's if you enjoy waiting in line behind a dozen other customers.  So not only are you wasting money buying parts you won't even use, but you'd have to pay someone to replace them with what you want.  When I build a computer, I only put into it what you really want or need... THE FIRST TIME.

Example (06-05-2001):

Celeron computer from compusa = $750
800mhz, 128mb ram, 40gb hard drive, 40x cd-rom, 4x4x24 CDR-W
Remove cd-burner, replace with 8x burner = $125
Remove cd-rom, replace with DVD-Rom = $100
                                                                    --------
                                                                    $975 for the computer you really want

Custom built by me with same specs:
 $464 for parts
+ 25% building fee
--------
$580, almost $400 cheaper

Plus with the name brand, you're stuck at 800mhz unless you get an overclock cpu which doesn't increase speed that much, or you have to upgrade the whole motherboard with one that IS upgradable!  My custom build is upgradable to PIII 1ghz, What would you rather do?