There's an article on CHOW right now about añejo tequila being a "hoax". It's at http://www.chow.com/stories/11023
I think that's a poorly-chosen term, and the article itself fails to argue its point very convincingly. But I do agree with its central proposition - that long wood-aging, with a few exceptions, is not as suitable for tequila as for other drinks (not just whiskey, which the writer chose as his focus).
I think there are three issues at work:
1. agave is a delicate flavor, easily masked by too much rich woodyness
2. to my taste (and this is strictly personal taste), excessive woodyness clashes with the flavor of tequila, in a way that it does not with other drinks. Not incidentally, it's important to bear in mind that tequila was never intended for long aging in wood. With a few exceptions, that's a new trend responding directly to demand in foreign markets (and, likely, Mexican yuppies).
3. I'm not convinced that tequila makers are fully skillful in how they do the wood aging. With some improvement, perhaps #1 and #2 will be overcome.
This is all even truer of mezcal. Especially #3. The añejo mezcals I recently tried in Mexico (from makers who produce stunning reposados) ranged from artless to horrendous turpentiney nightmares. You get the feeling that wood aging is done grudgingly and skill-lessly. Reposado's nearly always the smart choice. Also the more affordable one!
Of course, this is absolutely and totally a question of taste. If you like añejo tequilas and mezcals, that's certainly fine by me!