I have never seen a Flexifoil bladder go bad.... ever.

Some kite companies did seem to make a really bad move in 2004 with a different approach to bladder/valve attachment.
We had a lot of frustrated locals for a couple seasons, especially if it got hot.

Are you seeing a particular brand go bad? or just kites in general?
Brand new kites, or a couple years old?
I haven't had a problem in a couple years, since I switched away from the electrostatic or whatever method of the valve attachment.

I know Toby probably had it worse than any of us with his kites there for awhile.