I also have not had my tongue pierced, but my husband has. It swelled for the first couple of days and he ate softer food for the first 24 hours. It healed up well and never had any problems. He left it in for about 2 years.
I would also like to second lindsay_iu,
www.bmezine.com has great information on any body mods you (or your friend) might be interested in. They proved very helpful when I was making piercing decisions.
-wendi