Just started experimenting with RAW + JPG in the last week, and noticed a problem yesterday after importing my PM-keyworded photos into Lightroom 3. It's my old favorite, spaces in the keyword hierarchies not being ignored by LR on import, so a duplicate keyword hierarchy gets created - this is effecting only the JPGs, RAWs are fine. So, in addition to "Animal" as a top-level keyword, I'm also getting "Animal ", and since "Primate" is in the middle of a hierarchy, it comes in as " Primate " (with leading and trailing spaces). The final keyword in a hierarchy is imported with only the leading space.
I've decided to stop shooting RAW + JPG (for other reasons), but wanted to bring this up in case it effects other users.