This is the important question to answer. Apple should replace the battery for you if it gets little charge after relatively few cycles. The battery on my MBP started going bad after 11 months, with only 40 or so cycles on it. I took it in, the geniuses took one look in System Profiler at how the battery was performing, and replaced it right there. Even if you're out of warranty, I'd bet they might still be willing to fork a new one over to you.
cwa107 mentioned discharging often. In my experience, using the battery regularly actually helps it keep its charge. I'm fairly certain that my original one died because it spent the majority of last summer plugged in on a desk. The one I have now is still 97% healthy, according to Coconut Battery, and I've used it a decent amount over the past 3 months.