I've posted quite a bit about the tamron. It's a great lens, with my main complaint being AF speed. Here are a couple of threads where I've written things.
http://nikonrumors.com/forum/topic.php?id=904
http://nikonrumors.com/forum/topic.php?id=1576

Edit: also, pictures from an air show that were taken almost exclusively with that lens:
http://jonnyapple.dreamhosters.com/AirShow/

while i agree that the lenses are not in the same category, i think they ARE comparable given their prices. The 2.8's are huge while the 70-300 is much smaller and lighter, but from what i have read around the advantage in image quality is not clear-cut. Hence my question.

So while there are plenty of opinions on these lenses, can anyone give me an idea on how they compare?

Please do a forum search. The 70-300 and 70-200 lenses have been discussed several times. The f2.8 lenses are considered pro grade and can't really be compared to the f4.5/5.6 70-300.

Hey all, i've been pretty set on getting a 70-300 once my budget has digested the D7000, but a guest blog on Scott Kelby's site recommended the Sigma or Tamron 70-200 and forced me to reconsider.

http://www.scottkelby.com/blog/2010/archives/13022

I checked them out, and they can be found used for $600-$800. while the 70-300 goes for about $450.

I currently have a 55-200 so anything i get will be a considerable upgrade.

Anyone have any experience with these? its an intriguing possibility to get a 2.8 telephoto for this price. Are the 2.8's significantly better in IQ?

Any comparisons would be appreciated.