Anyone use teleconverters for bird pictures?

I've got a Canon 2 IS and am thinking of getting a 1.5x teleconverter from Lensmate. Are these similar to the old SLR doublers? Will I be losing a lot of light and picture clarity for bird shots? Any other suggestions to give closer pictures of birds?

Short and quick answer, yes, you will lose light (approx 1 stop) and reduce image quality.

Why lensmate? Does not Canon make a teleconverter for your camera (the TC-DC58B)? The Canon TC are, to the best of my knowledge, far superior to the lensmate stuff.

I just happened to have the lensmate site bookmarked. I'll be looking at the Canon teleconverters also.

I guess since my 2 IS zooms to 430 mm I'd be looking at something like a 500 mm or larger to solve the problem with a fixed lens approach.

Lensmate is a good resource. When I shot with my G5 they were the place to go. Their lens adaptors where way better than Canon's, and they offered viewfinder shots of the different tcons, showing how they would vignette, etc. And, as far as the Canon tcons being the best, not necessarily so. In the day, THE tcon to have for a G series was the Olympus.