It definitely can be a problem, catching up with an anime/tv series that already has a lot of episodes is a pain.
I think my limit for Anime is probably over 100 episodes, way too much time to catch up on.
For some reason, I think I'm more lenient with tv-shows - maybe because each episode is longer and tends not to have 'filler' or random episodes. I remember watching four seasons of Fringe in a relatively short time.
Saying that, if I start watching a program whilst it's still airing, and it doesn't bore me, then I continue on. I'm still up to date with Naruto now (after joining somewhere around episode 80), however I'll never start One Piece as 600 episodes is far too daunting.