Thought I'd do a "I've been using this for a while" follow up...
The Speed Booster has become a permanent part of my kit. I will often go out with just it attached to the EM5 and a couple of Nikkors rather than my standard kit. For those that liked shooting a camera such as the FM-2, this is the closest that I have come to that experience. And, just as shooting primes can be liberating, so can going all manual focus. It slows you down and allows you to think about focus points, composition, etc..
Anyway, if you have a stable of lenses from another system that you used to really enjoy shooting, I would suggest considering the Speed Booster.
Doug
Here are 4 from yesterday:
28mm f2 in the caves at Pinnacles National Monument
200mm f4 with Canon 500d diopter. An endangered species of frog repopulating the reservoir at Pinnacles.
28mm f2 at the top of the divide between the two sides of the park
200mm f4 with Canon 500d diopter. I'd love to know the species of this plant; it has a very unusual pattern in the seeds that I found appealing.