I grow lots of snowdrops in pots at present. Many don't appear to mind at all; some (like 'Rodmarton') have never flowered in a pot. For that matter, I grow a few tough little nivalis flore pleno in very dry and rather dark conditions under a tree - these rarely flower also. This season has been a particularly poor one for flowers, although a good year for bulb splitting and extra shoots. Last summer was unusually wet and not very warm - which I would have expected to benefit flowering. Last February, March and September were relatively dry, however.
My pots are outside all the time but moved to a shadier spot in summer. I don't plunge them so use unusually large pots, around 3 litre capacity. I feed them with tomato feed rather sporadically in March and April. The ones potted in 2010 are generally looking pretty miserable this year so it looks as if three years would be the maximum pot life without changing the compost and re-potting every two years would be better.
Roots never emerge from my 3l pots; in general root length and width are very dependent on the individual bulb.