There was a discussion on the 3/16/11 episode of Upgrd podcast. Bascially the gist of the debate was this:

Aside from the fact that it will take at least 10 years to break even, you're going to give $4600 to the new UA on the assumption they will deliver as least as much as you're getting now. Will they keep all lounges open in the cities you fly to? Will there be a devaluing of benefits in the future? What if UA merges with another carrier or experiences financial troubles in the future? On the other hand you're locking in the price now, so any increase in membership fees will not affect you. Most likely you will enjoy most if not all of the benefits you are enjoying now, but that's still placing a lot of trust in one airline.

Good luck.