My airline operates approx 70.000 sectors a year with the 737 (both 3/400 and NG aircraft).
Last year we spent a briefing item on bleed/press system due to Helios, but also because of the high amount cabin press warning in the first half of 2006.
We had 10!!! cab pres warnings in the first 6 months.
that is 1 in 3500 flights. A far to high number considering this is the last line of defence against loss of cabin pressure.
But in my humble opinion, I find it absolutely rediculous that boeing is allowed to still produce an aircraft with a 1960's design which I find an ergonomical nightmare to operate.
Spuis