ergophobe - 6:50 pm on Mar 1, 2013 (gmt 0)
If the options are too long to fit in a single pipe-delimited list
A little OT, but Lucy I thought I would pick up on this. I know you're using that as a rule of thumb, not advocating a piped regex over the [OR] statements, but for other people who might be reading that, I thought I would mention this...
In general, chained RewriteConds using [OR] perform better than a regex as benchmarked many years ago by Andreas Friedriech.
Now, many years ago may be a problem, since it's quite possible that mod_rewrite has refactored how it does regex searches. I don't know as anyone has tested it recently.