I have 5 trips in December. This is the [edit] fourth month in 2006 I have had 5 trips. That roster includes MIA, CPTx2, DXB, and JFK. Looking through the A340 Master Roster, around 15% of lines are 5 trips. I agree, most are 4, but the increasing number of East coast destinations means that 5-trip rosters will become more common.
[edit] My 2005 roster:
January: 4 trips plus 6 sims (Command training)
February: 4 trips
March: 1 trip plus leave
April: 5 trips
May: 2 trips plus leave
June: 4 trips
July: 5 trips plus 2 sims
August: 3 trips
September: 3 trips plus leave
October: 3 trips
November: 5 trips (standby roster)
December: 5 trips
Total (excluding December) 670 flying hours. I'm not on Extra Working and I don't do overtime!