Even Better Batteries
From an environmental perspective, I love rechargeable batteries.
Not throwing old used batteries in a land file is very nice thing. Also, when I some day put solar panels on my roof, there won't even be a carbon cost on the back end to get them juiced up. And, of course, there is the financial aspect that once you pay much less for a set of rechargeables and the electricity for a decent number of charges than you would for a comparable number of one time sets.
The one gotcha that the rechargeables I own have is that they don't really hold a charge. The main thing I use the batteries for is to power my small on and off camera flashes. When they are fully charged up, the NiMH batteries do a great job of this. The problem is that I don't shoot that often and with the battery leak, I pretty much have to plan a day in advance if I want to be able to use them. Otherwise, the last charge that I have given them is likely to be a few weeks in the past and the batteries won't have enough juice in them to provide more than a few bursts of light.
I recently saw about them in this Cool Tools post. Looks to have almost all the good parts, but the ability to hold a charge. I haven't purchased any yet, but they will be on the way soon enough. I'm sure the technology will continue to improve, but for me, this is a really significant improvement and hopefully will be the start of a sea change that also means less stress on the environment and less toxic shit leaking from batteries into our ground water.