Here's a wikipedia article that I found more comprehensible as someone who knows nothing about transactional memory:

http://en.wikipedia.org/wiki/Software_transactional_memory

So, as a Java guy, here's what I take this stuff to mean:

Synchronization blocks are implicitly pessimistic locking. Even if the probability of a collision is close to zero, we still make threads line up for admittance to critical sections.

Transactional memory allows us to employ optimistic concurrency. If any other thread modified stuff that is encompassed in your transaction, you get an exception.

This sounds much like the scheme employed by Hibernate to do optimistic locking for DB stuff. Am I thinking about this correctly?