From Canon T3i to Nex-6. Am I giving up some image quality?

I'm transitioning from a Nikon D200 based system to a NEX-6.

I may or may not sell the D200. I will certainly sell some of the glass and accessories; exactly which ones I'll decide over time as I gain more experience.

In terms of IQ I think the NEX-6 will be just fine. But there are (currently) some limitations and issues with the new system as a whole:

* No Arca-Swiss L-bracket yet. This is important to me but should be solved early in the new year.

* The selection of available lenses is somewhat limited relative to Canon and Nikon. The better NEX lenses are also overpriced for what they are. OTOH, the NEX does work really well with some of my old Nikkor's. When I say well.... I mean beyond my wildest dreams. They work great and MF with focus peaking is wonderful!

* Flash/lighting. I really want to see a compact flash with TTL, suitable for bouncing, and without any nasty adapters. Hopefully one will be forthcoming next year. I haven't yet decided which way to go for studio type work -- continue with Nikon flashes, switch to Sony, or go for studio strobes.

* Macro. I've done a tiny amount of macro work with my Nikon system. I'm not convinced the NEX is going to be strong on macro but it's low priority and I haven't investigated yet.

I'm very happy with the sensor although I should point out that I'm a committed RAW shooter and don't mind doing some work in ACR etc. Therefore, I'm not very interested in the out-of-camera JPEG's and haven't evaluated them.

Bottom line: I absolutely think the NEX is a viable replacement for the low-mid range DSLR's in general purpose shooting. The dramatic reduction in size and weight involves some compromises that I'm finding very acceptable. If you have specialist needs (e.g. macro or whatever) you need to check out the specific details of that -- don't assume the overall system is quite as complete or mature as those from Canon and Nikon.