Jumping the shark is a colloquialism coined by Jon Hein and used by TV critics and fans to denote that point in a TV show or movie series' history where the plot veers off into absurd story lines or out-of-the-ordinary characterizations, particularly for a show with falling ratings apparently becoming more desperate to draw viewers in. In the process of undergoing these changes, the TV or movie series loses its original appeal. Shows that have "jumped the shark" are typically deemed to have passed their peak.
No. If they completely changed up the formula of the show after the S4 finale, then maybe, but they went into the same old stuff right off the bat in S5.
I do think House this season as a whole has been much worse than normal, but it's probably going to get get much better (since there's only a few episodes left).
The problem with this season is that they've almost exclusively been focusing on 13 and Foreman, both of whom are really shallow and boring characters. The new team sucks in general, really.