Why even bother discussing incumbents? Gerrymandering and incumbency has assured >99% will be re-elected to the House.
Open seats are the only place where competition results in a chance to switch parties.
Examples: in 2002 even with redistricting, only 2% of incumbents lost, but 20% of the open seats changed parties
In 2004 2% of the incumbents lost (most due to redistricting in TX), but 17% of the open seats changed parties
2006 may be a banner year for party switches, as already 53 Republicans and 38 Democrats have hinted at running for higher office or retiring.
http://www.dcpoliticalreport.com/Retire06.htm
