I beg to differ, kind sir! Check out the videos on adapterplace.com. They're beautiful! In addition, the new adapter models (Letus, Brevis, RedRock, SGPro, etc) only lose about 1/2 - 1 stop of light. Not so bad.
The Letus Extreme is pretty solid - it's been serving me well since November. We'll be shooting a feature with the Sony EX1 + Letus Extreme this summer. Philip Bloom has been doing a bit of this...he has some HV20 + Letus shorts on his website - www.philipbloom.net
The world of 35mm adapters is a slippery slope. First comes the adapter ($1200ish), lenses, rails, follow focus, a tripod to support it all, matte box, HD monitor, handheld hardware, etc.
Be prepared to make an investment if you choose to dive into the realm of 35mm lenses (and you won't want to use autofocus lenses, the manual focus rings breathe too much)
You realise with an adaptor you will lose AF (and won't be able to alter the aperture easily), and 300mm on an adapter will probably be shorter than your camcorders own lens can do..?
I'm guessing you're not doing anything professional, in which case the better adapters (Letus, Redrock, etc.) can work well and look good. They do require some accurate manual focussing though, and may well be more hassle than you can be bothered with if you're just shooting your dog or something.