The only risk you take in that scenario is that your device may not charge as fast as you expect (or at all, if in use.) Same with the 3 different wattages of MagSafe adapters.

But there will be no damage which is more important. My iPad simply slow charges (1A) on my old iPhone & my newer/current Samsung & LG 1A phone charger. Meanwhile my iPad charger works on all my devices - retired iPod Mini, my old iPhone 3G (now iAlarm Clock), Samsung Admire, LG Motion 4G, iPod Touch 7G. In the latter case, charging isn't any faster of course since the devices will only pull 500mA (Admire) or 1A.

The only chargers that I have that won't charge my all of my modern iDevices are old ones meant for iPods (500mA, no signal on the data pins) and my old Belkin iPhone car charger doesn't work with my iPad (Probably only 500mA w/ signal for iPhones. I'd have to check).

Another interesting tidbit: It appears that my car's Pioneer DEH 9400 head unit (aftermarket of course) seems to inform my devices that it can supply 1A of power through its two USB ports. This is the first time I've seen that outside of dedicated chargers and Macs (I assume of course that some PCs do this as well but I haven't seen one yet).