A few people I talk with regularly on mIRC were talking about equities, and as part of their conversation, introduced me to this all in situation interactive quiz:
http://weaktight.com/racequiz/Omaha
I have to say, i'm pretty impressed by it, and am amazed I haven't heard anyone else talk about it considering it has been online for a few years now.
I figure it will be of great help to PLO players who want to get a better feel for how their equity stacks up against known hands on known boards. Im sure it can only help you make good calls and folds :).