A little late, I know, but I wanted to add that you don't have to pay the penalty for failure to pay estimated tax if the tax you pay this year is 110% of the tax you paid last year. Doesn't help the problem of it being a "bite" all at once, but it can cut out the penalty.
We've also upped my husband's wihholding a bit since he's not self-employed. Somehow it's less painful if you never see the money. Of course, we'll need to adjust that if our refund is large -- I'd much rather we got the interest on our money for a year than the IRS getting it.
This is my first year of full-time self-employment, so I know how you feel. But I've been doing it part-time for years, so at least I'm not trying to figure out the rules -- just trying to estimate income is stressful enough!