Not particulaly sure why i'm replying, on the most part it seems like preaching to the ****witted.
There's an actual very real danger with tongue piercing, no, it's not cancer, i won't go into explaining why, i don't think i should really waste my time explaining it, but the danger is facial paralysis.
Paralysis is only a problem if you have a bad piercer, and yes, it's permenant. If they pierce in the wrong place, or pierce at all (There is a chance that you won't be able to have a tongue piercing at all) they can really screw up and for the rest of your life your face will be broken.
But that's a very very very rare thing, as piercers in general are competant and know what they're doing. But that's also a very good reason as to why you should go to a good piercer, not a crappy one just because the crap one's cheap.
As for getting it done, sure, knock yourself out, i've had mine done for some 5 years now, other than the initial healing, never had a single problem with it.
As for the initial healing, it varies from person to person. It's impossible to say how your body will react to it, all i can tell you is what *could* happen, but then again, there's a small chance that none of them will happen.
The main one is the swelling of your tongue, this could last anything from 1-5 days, and believe me, it's very uncomfortable to do anything, even swallowing anything, eating is near impossible and drinking is painful as hell. On the most cases, people rarely swell for long, but it could be a long thing, i personally had 5 days of swelling, i didn't eat for all 5 of them, which looking back on it, is a bad idea. And then there's the usual things, bleeding (Not too common really), the usual generation of crap that you need to regulaly clean, general stinging or aching pain inside the piercing, and so on. But realy, the swelling is the bitch here.
And finally,
bmezine.com will answer any question whatsoever about piercing.
EDIT: And from that site,
here is a summary of any risks and such involved with tongue piercing, and for all you "OMGZ CANCAR" people,
read this.
"While there may be fictional theoretical anecdotes illustrating this, there is no evidence supporting this theory."
"To be clear: tongue piercing does not lead to cancer!"