Duuuude's, I know this is an old thread but I just had to reply.
I get the exact symptom that the OP is talking about. The strange thing for me is that I don't experience it at all (or at least notice it) WHILE I'm actually ON the drug, but after I wake up and for like half (sometimes the entire) the day I have this weird taste-thing going on. It's almost like my tongue is coated in something that makes everything I eat/drink feel/taste weird. It's definitely not just a taste thing alone... there's also a texture sensation going on. It really feels like my tongue has a film over it... or almost like my saliva is altered and it's making my tongue feel this way. I bring up the saliva part because I notice that I always try to spit as much as possible while I'm in the shower to try and get this "taste" out of my mouth.
How noticeable this sensation is is directly dependent on how much/little xanax I take. I RARELY ever use Xanax nowadays but back in the day me and my buddies used to take a bar or two (2-4mg) and just black out for the night. The next day I would wake up and try and eat and this sensation would be SO bad that it would actually cause me throw up sometimes. The sensation itself would make me nauseous for the entire day when I did that much xanax. On the opposite end of the spectrum, if I took, say, half a football (.25mg) for whatever reason, I would still have the taste-thing going on the next day but WAY less intense and no nausea at all.
It's a really freakin strange sensation and it is quite annoying (and one of the things that keeps me away from xanax... which I'm thankful for in a weird way lol) as it can completely ruin your appetite.