THX is basically a set of standards devised for George Lucas, originally to improve the sound in cinemas. THX amplifiers, for example, process the sound to make the treble less harsh, plus lots of other 'tweaks'.
The glasses are for use with the THX Optimiser, which is a series of test sounds/images to set your television up 'correctly'. Specifically, they are used with a colour test.
The THX Optimiser can be found on Lucasfilm DVDs, and, I think, Pixar (it's usually in one of the extras or setup menus, and I found it easy to miss as it appeared to just be a logo!).
To get the full benefit of THX modes on an amplifier with a THX logo on it, you would really need to buy a set of THX-certified speakers (which aren't that cheap). THX used to recommend (I assume they still do) that you only switch on THX processing with movie soundtracks. THX speakers are good for THX, but maybe not so good all rounders, with 'ordinary' surround sound, or plain stereo.
The THX logo means that the equipment (and some DVDs etc) meets THX's strict standards - it doesn't necessarily mean the equipment is better than non-THX (although it should be pretty good).
www.thx.com