Looks like "ambassadors" of each brand are starting to show up to aid you in your buying decision..
Like what Galdor has wisely said, whichever brand you go for is really not that important. You can see beautiful works in the subforums of each system here.
How good built-in IS is would be a topic that has been debated to death in photography forums. I feel that while IS is rather useful in most general situations, there are times when a camera with no IS but 2-stops less noise at high ISOs would work better, e.g. if you want to freeze moving subject(s) in low-light environments, you cannot do it on an olympus without a) using a lower ISO+IS, leading to motion blur on your subjects, or b) using a high ISO eg. 1600 to freeze motion, but leading to a noisy picture. I do use noise removal software, however removing heavy noise will bound to incur some image detail loss.
If this is too technical right now i apologize, but basically i am trying to say IS is a "convenient to have" feature in some poor light situations. You should probably be bringing a tripod and ring flash for serious macro work anyway.
And o yea the dust reduction system in olympus works well, i hardly ever encounter problems with dust