I would pull the trigger on this one for a few reasons.
1. Holliday is due for a drop leaving a great hitters park and going to a pitchers park.
2. Utley is HURT.
3. You are getting the best player in the deal (and in the league), who is also the youngest player in the deal. He'll be someone you can count on for years (he is 5 years younger than Utley and 4 years younger than Holliday). On the flip side Oswalt is the oldest (and worst) player in the deal, but when you are dealing with a 6 keeper league, you have to realize that there is a much higher replacement player than during the season. Granted for 2009 alone, you can consider those players compared to normal replacement levels, but when you are considering your 2010 and beyond keepers, you may find that upgrading Oswalt becomes quite feasible, especially if he eventually starts declining seriously. Holliday and Utley may decline (in a few years) to the point that they are near borderline keeper status, but it will be harder to decide to keep some younger high upside keeper in their place. You can cut your ties with Oswalt in a few years, and still end up being the big winner. If you end up cutting your ties with one of the other two, you'll be the bid loser for sure.
i'm the guy that puts the "nip" in omnipotent...