Great question J.! What a hot topic. All the data seems to agree that kids really shouldn't watch tv until they're at least 2 and then as little as you can help after. My father's a 4K - 2nd grade principal and my mom, sister and cousin are elementary teachers and they can really tell by school age which kids spent more time in front of the tube. The flashing and quick movements really do have an effect on development and attention span. Not to even get started on all the ads - even public tv's sponsors have gotten more and more "commercial". Just because Baby Einstein and other companies gear things towards babies and toddlers doesn't mean it's good for them. They're trying to sell products after all.
As a pregnant (and morning/all day sick:) mom of an energetic 2.5 year old I truly sympathize with the temptation. When I'm getting supper ready or feeling especially queasy we do watch Curious George, Sesame Street or pop in a Scholastic video. But I try to keep it to half an hour, closely monitor content (how are the characters treating each other? is anything scary?) and check in every 10 minutes or so to ask questions. Not that he wouldn't watch more given the opportunity - but I realize that it's more of a convenience for me than all that beneficial to him. It helped that his Papa and I didn't watch tv until after he went to bed, so it wasn't something we had to re-train ourselves on as parents.
One thing we've done instead is to listen to music or books on album/tape/cd. It's still entertaining but uses more imagination/is more interactive than tv, which is really passive. And still engaging enough to give you a break when you need one. Sing along songs, counting rhymes, classic stories, some which have books to read along with. Every kid's different, but Finn's always loved being read to and now at 2.5 will sit for long periods reading to himself even without the audio (like right now as I'm checking email/writing this:)
Every family needs to decide what's best for them, but I figure he's got his whole life to watch tv, why start earlier than necessary? Good luck mama!