Sometimes the failures are catastrophic,  and other times they are latent
 (ticking time bombs - these are the failures that really suck). Reworking a
 board lowers the reliability of the parts on it - even innocent bystanders. 
This is something I have _never_ observed. I've reowkred many boards (OK,
small sample, but...). I've desoldered ICs and soldeed them back again.
And I have never noticed a larger failure rate for stuff I've repaired as
agaisnt stuff I haven/t
-tony