OWC SSD freezes regularly
I've got a OWC Mercury 115GB in my MacBook (2007) and encounter the same problem although never as severe as you describe.  It was fairly frequent (multiple times an hour) while I was running FileVault2 but once I turned it off, it became much less frequent (perhaps once an hour).  Normally, I see a complete freeze of the system, not just the application, for about 30 seconds.

SSD garbage collection seems like a likely suspect.  In theory, the Sandforce controller plus the larger scratch pool on the OWC drive makes TRIM unneeded but if GC is the issue, maybe TRIM would reduce the frequency.  That said, I read lots of reports of people seeing a similar problem when they hacked their system to support TRIM with 3rd-party SSD's under Snow Leopard.  I stopped following the discussion when I upgraded to Lion so I don't know anything about current experiences.

I try to keep at least 30GB free.

5+ hours seems like a crazy long time to do a Lion install so maybe you have a different problem.