Here's what I did/do when I first got mine. At first the battery life was really bad. Sure I was playing with it a lot but only lasting like 5 hours, the battery meter jumped all over the place between having it plugged in and having it not plugged in, etc. A friend mentioned he had similar problems with his ipod when he first got it. What he did was just use the ipod for a little bit, just as long as it's no more than like 75% charged according to the meter. Then when you go to bed plug into the charger (i used the wall plug). In the morning it should be fully charged, or think it is. KEEP IT PLUGGED IN. Restart it (hold down the sleep/wake button until the "slide to turn off" shows up) and leave it plugged in until it says it's fully charged again. Mine thought it was fully charged again after only a few minutes, but I guess it could take a while so you may have to do this completely over a few nights or take it to work and plug it in there. I think the key things are that you leave it plugged in overnight even it says it's fully charged within a couple hours and that you leave it plugged it when you restart it. Worked for me by YMMV.
I did this a couple nights and now the battery meter is pretty stable and I've gone for a couple days without worry. I don't use the ipod part of it too much but the biggest killer of battery life to me is mobile web. Even now browsing around will just kill the battery.