If I work (in the U.S.) for an annual salary with standard benefits, and I interview with a consulting firm in which pay is hourly and total cost of benefits are deducted from the salary, what is a good heuristic for figuring the hourly equivalent to what I'm now earning?
given a 40 hour week at 52 weeks minus 3 weeks vacation and 2 weeks sicktime makes 40 hours times 47 weeks. That's 1880 hours. So if you use a 2000 hour figure (counting in some overtime) and rounding up you're pretty close. Of course you then have to take the cost of all those extras and add them to your salary.
So if you make $50K a year with another $10K in standard benefits (just example figures) and the cost of those benefits remains the same, you end up at an hourly rate of $60K/2000 of $30.
That's if it's for a paycheck of course. If you're going to have to pay all the things normally paid for by your employer which are not on your paycheck you have to add those as well. Such things can easily double your cost (and keep in mind that the tax and social security rates will differ when your self employed, as will the cost of insurance).