Well, after doing a quick search, I found the toxic chemicals in the leaves are solanidine, tomatidine, and solasonine. Exposing mice to these chemicals caused their liver weights to increase (I'm assuming this is a bad thing, meaning the liver is overworking to get rid of the toxins, or becoming damaged).
Here's one abstract:
http://www.ncbi.nlm.nih.gov/pubmed/8613903
Here's another one noting that ingesting these compounds caused mice to miscarry during pregnancy:
http://www.ncbi.nlm.nih.gov/pubmed/12453729
Here's the MSDS on solanidine:
https://www.mpbio.com/includes/msds/...33-EN-ANSI.pdf
The toxicology discussion is in section 11 and notes that solanidine can cause nausea, vomiting, skin redness, edema, and in high doses, unconsciousness.
The lethal dosage is not determined. My guess is no one wants to volunteer to take a lethal dose of tomato leaves.
The MSDSs on the other 2 chemicals state they don't have enough information on how it affects humans to be able to discuss toxicology in detail.
So, I would not eat them.
Based on this admittedly very limited information, I would highly recommend that anyone who is pregnant or nursing definitely not eat tomato leaves or plant matter (except the tomatoes, of course), unless consulting with their OB or midwife first.