Practically every seakayaker down here in Tasmania uses electric bilge pumps (everyone uses sails as well but that's another story). They are fast, enable you to keep your deck on when in operation, thus preventing another dumping wave filling your boat up again and you can keep using your paddle thus making you much more stable.

The downside is not the weight of the battery as you can source some pretty light weight units that will keep your pump running for a couple of hours or the reliability of the pump which seem pretty bomb proof, the weak point is the switch which even if marine grade always fails eventually. Some people just carry a spare switch and set up the wiring so that it can be "hot swapped" out when it fails. Gnarly dog, who someone else has linked to, has some pretty good ideas about how to get around the switch problem and I'm going to try out his magnetic switch idea on my current build.

The other weak point is the battery terminal, if these are not protected they will eventually corrode. In my group the standard practice is to solder solid core copper wire to the terminal and cover the terminals in epoxy.

I did consider a foot operated bilge pump for a while but the slow pump out rate and the amount of modification required turned me off.

Oh and if your going to rely on a mechanical device to empty your boat always carry another method of bailing your boat, such as a large sponge or bailing cup as anything made by man will fail eventually.

My 2 cents