In my opinion, the worst part about using rechargeable batteries was always the amount of time you had to wait for your batteries to recharge once they were used up. Apparently, I wasn't alone in my thinking, because Energizer recently came out with a 15 minute AA / AAA battery charger.
I use reghargeable batteries in everyday things like flashlights, MP3 players, remote controls, and digital cameras. These are all devices where I really don't want to be forced to wait a full 8 hours for my batteries to recharge. With this charger, I'm usually able to get everything back up and running in right around 15 minutes, which is really amazing when you compare it to the amount of time that was required just a few short years ago.
This charger allows me to insert anywhere between one and four AA or AAA batteries at any one time, and since the current required to charge a battery to full capacity in 15 minutes can produce a lot of excess heat, they've also incorporated a miniature fan inside the charger to keep the batteries cool.
There's an indicator light on the base of the charger that changes from red to green when the charging process has completed. Once the light turns green, the charging process will cease, however the fan will continue to run for several more minutes after that. If you leave it plugged in for an additional 5 minutes or so, I've noticed that the fan will eventually shut off as well.
Depending on the capacity of the batteries that I'm using at the time (i.e. their "mAH" number), I've found that the charging process can actually take a little more than 15 minutes, so don't expect that number to be exact. It's more of a guideline.
Thus far, I haven't really found any major downsides to using this charger. I've read a couple of different opinions that say this charger may not charge batteries as completely as a slower charger, but I guess I'd rather have my batteries charged to 96% capacity in 15 minutes, as compared to having them charged to full capacity in 8 to 10 hours. I've also read that charging the batteries in such a short time may reduce their overall lifespan, but even if they last only 300 cycles as compared to 500, I think the amount of time that I'll save is well worth that difference.
Now that they've eliminated the inconvenience of waiting hours for batteries to recharge, there really is no reason that I can think of, not to try using rechargeable batteries.