IDE = Drastically slower, more power consumption, jumper hassles, and yucky wires.
S-ATA = Much less power consumption, NO jumper hassles, much smaller neater wires, cheaper, hot-swapping, and a lot faster.
S-ATA HDDs sometimes have no jumper pins (unlike IDE) and possess smaller power and data connections. S-ATA HDDs will usually always have S-ATA written on them somewhere. It's pretty difficult to confuse them, IMO.
IDE HDDs always (I know no exceptions) have at least 8 pins (possibly 6 for older ones?) for the jumper settings, a large 40-pin data connection and a standard 4-pin molex connection for the power. These are easy to spot.
Some motherboards support IDE and S-ATA, while others support only one or the other; you can find out what your motherboard supports by looking online, on the motherboard, or on your motherboard's manual. To identify the motherboard's connections, it's as simple as:
S-ATA motherboard connections = Small.
IDE motherboard connections = Large.
About as simple as that, and you can always Google for more info if you need it.