Personally I use a Canon 600D which has a crop factor of 1.6X with a Tamron SP90 (90mm f/2.8), that gives 1:1 at about 11 inches minimum focus distance. In general, this is good enough since I can always crop the pic if the subject is really small, e.g., < 1 cm long. If I want a larger than 1:1 image, then I clip on a Raynox 250 that brings the minimum focus distance down to 4 inches or less, and it does not really destroy the image quality. The 2 pics here will show what I mean. Taken at ISO400, f/11, 1/200, diffused Yongnuo flash, handheld, contrast boosted 5%, no other adjustments.

1st one is uncropped and only downsized for LYN :
http://www.flickr.com/photos/85704451@N04/10472915854/

2nd one is cropped and further downsized :
http://www.flickr.com/photos/85704451@N04/10472919106/

So I always bring the Raynox around just in case I need it. DOF is super thin, but it should be better on a m43 sensor