I had to quote this to remember it all - :D
I do agree that prebuilt pc's are fine for the 'general' user - they do not have the experience to order parts that are compatible or know a CPU from a PSU, for those people it is fine -
BUT, people are getting more knowledgeable and are willing to have a go at building a PC - as for it taking more than a few hours, I DO NOT AGREE the one in my PC Build took 2 hours and that includes installing the OS - they are easy to put together.
People like DELL do offer good systems, and yes you can get them 'customised' but the parts are still limited -
If you build a PC you get SPECIFIC parts from major manufacturers:-
LIAN LI CASE
INTEL CPU
ASUS MOBO
OCZ RAM
NVIDIA GPU's
SAMSUNG HDD
you add a decent CREATIVE sound card, you get an OCZ or CORSAIR PSU - an OEM version of an OS and away you go - put it all together, any problems along the way then WE are here as a PC HELP SITE, and we have helped many people along the way -
you compare a system like that compared to DELLs offerings.
As for Dells and HP etc not breaking - have you never worked in an office - I see about 2 a day being carted out on a trolley (and these are 1 year old Vista jobbies) - they DO NOT last any longer than a pre built PC - as for warranty you get a year with most manufacturers and some even have lifetime warranties on components - My BFG GPU is covered for 10 years!