• turn down the heat in the kitchen at night
• turn down the heat in the MBR during the day and at night

1. Is this a good idea?
2. Are programmable thermostats good for radiant heat?
3. Do i need a particular type?
4. What kind of savings can i expect (i.e., will the cost of the thermostats be offset by the savings?)

It depends on whether you're heating a 4" thick slab or just a tile/hardwood floor above a plywood substaright.

Are there air registers in these rooms too? Meaning, is the floor warming system the only source of heat or is there forced air as well? I'm presuming that it's hydronics, not electric radiant, correct?

You were probably correct the first time. Hydrostatic would be correct for a forced air, hot water system. Hydronics are, generally speaking, water in tubing in the floor, like your kitchen and baths.

If you turn down the floor temp to say, 65 degrees, how long will it take to bring it back up to a temp your happy with again. The possibilty exists that just leaving it with a 2 or 3 degree set back may be more 'satisfying' because the two costs end up being the same. That is, turn it down and it takes 2 hours to bring it back up vs. leaving it on and it only runs for and hour overnight to maintain. It will take some playing and a couple of months bills to find that out.

I would still like programmable tstats installed though. Control over the system is always a plus. Providing the floor isn't in and the ability to install sensors  in the floor is available.