Last year, from what I heard, this was done because they had to shoot the back half of the season after it did so well. But now this seems to be a trend. "Lost" and "Jericho" are following the same formula. A tactic seen more and more with "serialized" dramas.
I, personally, like this. Sure it can be frustrating to have to wait so long. But consider that most networks will take about six weeks off (from airing new shows) between Thanksgiving and New Year's anyway. Pushing the return dates out to February or March might be a little extreme though.
As for "Prison Break", Fox is in a bind since they are now married to the January start time for "24". So they have to find time to air four hours of that during a week in January, and then drop shows back into place. And Fox seems to be supporting "Justice" as well. So they have "24", "Prison Break", and "Justice" fighting for 2 hours of Monday night real estate. And "24" will no doubt retain its spot. As I recall, the "24"/"Prison Break" combo did pretty well last year.
Get ready for an intense three weeks "Prison Break" fans. That sort-of finale will probably be a doozie.
And to make this clear. Nothing indicates that this is in any way related to any ratings issues. It appears to be a planned hiatus.