One of the biggest drawbacks or one of the most common claims from its detractors to the micro four thirds format, like the Olympus OM-D I recently bought is the lack of Bokeh that can be achieved with such a small sensor.
First, for my friends who are not up to speed on camera technical terms, Bokeh is the background blur effect used often to separate the subject from the background. This Bokeh is primarily tied to aperture. The wider the aperture the more Bokeh you can achieve. But... this effect is also related to sensor size. Full frame cameras like the more expensive Canon and Nikons achieve greater Bokeh at the same aperture than crop sensor cameras like the Canon 7D, which I've been using for the past 2 years, and even more so than micro four thirds cameras that I'm using now.
As you can see by the photo above and below, you can achieve great Bokeh with these cameras, but it admittedly it is more difficult to get that shallow depth of field look. The lens I used for these two photos was a 14-150mm lens. The top one was zoomed all the way to 150mm and set at its widest aperture of 5.6, and I got as close as possible to the flower. By doing this I was able to achieve a very shallow depth of field. The one below was at only 34mm and the aperture was at 5.1. As you can see the background is not as blurry. By the way, that was my intended look; I wanted the flower to stand out as the subject, but also wanted to be able to subtly see the Japanese house in the background
Bottomline, is if shallow depth of field or Bokeh is a strong theme in your shooting style, it is more difficult to achieve with the Micro 4/3rds cameras. Fortunately, as this format grows in popularity with serious photography enthusiasts ( and some pros) the manufactures are releasing high quality, fast lenses with low apertures so the Bokeh problem is becoming less of an issue.
Over the next couple days, I'll post some more images with Bokeh as the theme. All these images were taken at Gotemba near Mt Fuji. Tomorrow with by the famous Japanese cherry blossoms.