I decided it was time to upgrade my camera body, so this being the case I thought I may as well go the whole hog and get a full frame camera. The camera arrived on Monday and I'm thrilled to bits with it. Apart from all the new bells & whistles I've got to play with it takes a great photo.

Ok enough pre-amble. My question relates to lenses. I have some lenses that are full frame compatible but most I own are APS-C lenses, including my general "walk-around" lens. Of course the new camera switches automatically to APS-C mode when I attach one of these lenses, (except in the case of the Sigma lens, but I can live with that) and they take great sharp photos, as they are quality lenses. One could leave it at that and say "The camera is taking good photos now. What are you worried about?" But from a technical point of view, am missing out on much by not using full frame lenses with the new camera?