Photography: Camera sensor size difference

After much deliberation I recently went for a well looked after second hand 5D and I don't regret it at all.

It depends what your priorities are. If image quality, 5D. If you want video as well, 550D. Either will take great photos, but for me the viewfinder, full frame sensor and fantastic IQ made the 5D the right choice for me - it's just a great photographic tool (but I'm not interested in video).

The price difference between the 5D and MkII is painful.

After thinking it looks like I'm going to go with the 5D

I always think oh video would be good, but honestly how often am I going to use it?

the 5D looks and feels imo much more like the film cameras I'm used to.

The only thing which puts me off is the fact that the 5D's are 3-4 years old now, is the technology old at all, is there anything I should be looking out for when buying one?