Ah, yes - that was another reason as to why I converted mine to a Blackbook rather than getting new white case parts to replace the cracked ones - after 3 years my MacBook had gotten pretty grubby, even though I cleaned it on a regular basis. As you said, the black case hides the dirt and stains pretty well.

In regards to battery life - my original battery still got about 2.5 hours up until it started expanding in November. It had somewhere around 300 cycles on it from memory. I'm now using an even older battery that originally came from a Mid-2007 MacBook that got scrapped for parts, and it actually gives me 3 hours. Has 583 cycles, apparently. Pretty damn good for a machine that'll be coming up to 5 years old this year.