Celerons are cheap. While they don't meet the same performance levels as the Pentium II, upon which they are based, for "serious work" due to their smaller cache size, you can't beat them on a price/performance ratio basis. And, although they have a smaller cache than the Pentium II, the fact that it runs at a higher speed means that for many people running them, they're about as fast as one. When you combine their low cost with the fact that they tend to be very overclockable and can perform in SMP mode with a small modification (which happens to be built into the BP6), you end up with the possibility of getting an immense amount of computing power for very little money.