Yeah you will notice the picture start to wig out if they are too close. It really doesnt damage the TV unless you were to leave them there for a long time, but who would?
Shielded speakers can be placed on top or along side a TV with no problems. The only time you need a shielded speaker is when you are using a CRT (tube type) TV. Projection and LCD TV's are not affected by speaker magnets. In general plasma TV's are not affected but you might run into a problem with certain plasma TV's.