The first time I built an Abit BP6 with dual Celeron 300's (overclocked to 450, naturally) I felt like I was getting a supercomputer for cheap. The performance increase going to dual-core was massive, and getting to use the cheap Celerons instead of the crazy-expensive Pentium II's paid for the rest of the system all on its own. The late 90's/early 2000's were exciting times for system builders.

Now? Meh. I still build my own, because you can spec out exactly what you want. But there's no longer any compelling performance reason to do anything beyond stock cooling and stock clocks.