re: Hourly vs. Salary - IT Developer

Ask them the average work hours per week for the position.
Make sure they commit (in writing) to a 40-hour work week (if they are legit, they'll have no problem doing this as it's expected). Ask about "opportunities for overtime", how overtime is compensated (if they allow OT) and "clocking in/out" procedures even for breaks.

I've seen far too many poor managers manage through making policies which impact a broad swath of people just to avoid having to deal with a person specifically and this often involves time. This can be something like everyone taking a 15-minute "smoke break" has to sign their time in/out in a logbook at the receptionist's desks to mandating a 5-minute window prior to assigned report time for people to log in (ie: not any earlier than 5 minutes before the time you are to be there and not a single second after) and/or a 5-minute window after you are to clock out.

Hourly jobs are common up and down the food chain but usually they pay less than salaried positions (the trade-off being the vast discrepancies in hours from week to week like you mentioned). This big of a jump TO an hourly makes me wonder if you aren't getting hosed at your current job, this company is desperate for workers (or they are desperate for you) or they have enough of a history of management problems that they have to pay so high just to get applicants.

Try to ask around about the place and the management or the department you would be in while you are waiting to hear back from them.