If transparent persistence is persistence where you don't need to make any special cases in your object model for persistence puporses (somehting nothing actually does), maybe translucent persistence is when you get a couple odd restrictions that enable vast improvements. JDO 1.0.1 would fall in this category with the PersistenceCapable pucky.
I have been thinking more and more about doing PC like behavior as it opens up so many options for optimization it is downright silly. Compile steps are annoying, but... acceptable. Aspect systems provide the needed hooks in a much better API than straight bytecode enhancement. Seriously thinking about things like that. A huge thing is the simple question "is it okay if when you store a transient object you get back a proxy which is transactionally bound instead of the same instance you stored?" If the answer is yes we can blow toplink/hibernate/ojb performance out of the water =)