i havent any experience with any tamron lens, nor the 400D. But i hear it had a few weening problems when it first came out - people were complaining of weird noise and output from the sensor on these very forums as i remember it. Not to say you shouldnt get one, but use the store return policy without any qualms, should you find it isnt up to scratch.

i moved to a dslr (30D - so it was rather a large leap ) from the A95 and found that all i really needed was the kit lens and a macro lens to continue doing what i liked doing best.  But if you want medium telephoto ability then i suppose that 200mm will do you good.  I have the Canon EF-S 17-85mm IS USM and found that i never used my telephoto (i have a 70-300mm that saw its first outing in about 6 months for the eclipse) for the shots i did before i got hooked on my two prime lenses. Obviously a lot of changing lenses is involved shooting with primes, but before i did that the 17-85 never really left my camera, and if you are a bit on the shaky side the IS is a lifesaver!

As Michael said, go into the shop and try some of the other lenses out and see what you think...

"In every colour, there's the light.
In every stone sleeps a crystal.
Remember the Shaman, when he used to say:
Man is the dream of the Dolphin"

Rich Meadows Photography