It was during the Johto Saga that I kind of got behind on watching the anime, and I just stopped for awhile. There's still a big chunk of episodes during those seasons in Johto that I haven't seen yet. Then again, I don't think I missed much given all of the fillllleeeeerrrrrr Johto had. It was only two or three years ago when I finally watched all of the Silver Conference episodes that I hadn't seen already.
When the Hoenn Saga was about to begin, that's when I got back into watching the anime again and followed it pretty closely for awhile. There was a time in the middle that I got behind, but it wasn't as bad as with Johto.
Ever since Sinnoh, I've been following the show consistently. There were a few episodes in Best Wishes that I missed and haven't caught up on yet, but I can't be bothered. As I will continue to watch the anime, I have to say the Black and White season has been kind of disappointing to say the least.