but the part about stretching preventing injury is definitely true. Here's an excerpt from an article that suggests heat works better.

Many researchers have suggested that stretching regimens represent the ideal method for improving hamstring flexibility. While this approach certainly seems to be reasonable, the research concerning the effect of stretching on hamstring elasticity has been equivocal. For example, one investigation determined that 30 seconds of static stretching significantly improved hamstring flexibility (4), while another study found that a combination of static and proprioceptive-neuromuscular-facilitation stretching improved torque production by the hamstrings but failed to enhance hamstring flexibility at all (5).

Another preventive approach
that is very unlikely to yield
success is stretching. Almost all of
the studies that correlated
strength deficits with injury risk
failed to find a correlation of
flexibility with injury risk
(Bennell et al, 1998, Burkett,
1970, Orchard et al, 1997,
Yamamoto, 1993, Heiser et al,
1984). Also, recent randomised
controlled trails have placed
major doubt on stretching as a
method for injury prevention
(Herbert and Gabriel, 2002,
Shrier, 1999). A major
confounder for flexibility studies
is that athletes with greater
`speed' show greater flexibility
and almost certainly have a
higher injury risk. Distance
athletes have reduced hamstring
flexibility and may actually may
derive a performance benefit
from this (Wang et al, 1993,
Jones, 2002), while it is known
that hamstring injury incidence
declines as running speed is
reduced (Bennell and
Crossley, 1996)