With only a couple months of expenses saved up, you're taking a big risk. It sounds like you could live a couple months off savings and a few months off contracting. I have no idea what the economy will be like in 6 months, but you will probably not have enough revenue from your web startup to fund yourself. You may from contracting - good developers always seem to be in demand, even in bad economic times - but the contracting market is hurting from the economy too.
OTOH, there're risks to staying in a dead-end job too, particularly to your sanity. It sounds pretty bad. And sanity is not something you should sacrifice for money.
Honestly, if I were in your position, I'd do it. But acknowledge the risk you're taking and take steps to mitigate it. Cut your expenses to a bare minimum and line up contracting jobs well before you need them. It really sucks looking for work when you're running out of money - you're in a much better bargaining position if you've got income and plenty of savings.