I've been one of the guys that has said that the Pats will put him on IR, but that is based upon the assumption that he wouldn't be ready to contribute till halfway through the season. If he is ready to go by pre-season and is better than what the Pats have, in the way of returners, then toss him in there and run a few back.
Frankly, I saw the genius of his selection in that he isn't needed this year, already has a reason to go on IR, the roster spot is likely needed in other spots, and that he turns out to be the first Patriot pick for 2010. Nothing wrong with getting your picks in early, in a sense.
PUP seems a better option than IR so that he can at least practice with the team later in the year (even if he's inactive weeks ~10-17). The reality is that by week ~9-10 they'll be at least a couple players on IR such that using the 53rd roster spot at that point on Tate won't be detrimental to the team.