Casdave has already given some good info, so i’ll try not to be repetitive.
Back when i was living in Florida, my bike of choice was a BikeE (due to the hills and traffic, it’s not the most practical thing to have here in San Francisco). They’re definitely slower going uphill, you but tend to make up for it on the downhill. I did some touring on it through central Vermont – pretty hilly – towing a trailer, and didn’t have much trouble at all. Coming down one particularly long descent, i looked down at my computer and it read 57 mph!
I know all about riding one in the heat, having gone through a couple of Florida summers on the thing. It really wasn’t bad at all. Sure, my back got sweaty, but no more than the rest of me. It wasn’t as bad as riding with a backpack on.
One thing that hasn’t been mentioned is why recumbents, as a whole, are so much faster than upright bikes. In addition to the aerodynamic advantage, you’re using your leg muscles more efficiently and you’ve got the back of the seat to push off against. Furthermore, the frame design of many recumbents (the BikeE’s single beam frame is a prime example) allow them to be much more rigid than a standard bike, so they deliver a lot more power.
Unless you live somewhere where biking is very common, you will get a lot of looks. This can be a good thing or a bad thing, depending on what you make of it, and where you happen to be at the time (ie, if you’re riding through a not-so-nice part of town and some big guy starts chasing you demanding you let him ride it… but chances are you’d avoid such areas anyway ;)).
It takes a little getting used to, but after a little while, you’ll be able to ride a lot longer on a recumbent than on an upright bike. You won’t suffer from the numb crotch syndrome, your back won’t ache, etc. Also, a recumbent works your abs a lot more than an upright bike: ride one every day and you’ll have no trouble with situps!