Like nsayer, I have never had totally acceptable service from the Microcell. I've been using one for 1yr 9mo.
Most of the problems seems to be incompatibility with the iPhones, particularly when trying to place a call and it fails the first attempt. Also the iPhone 4S randomly drops the connection to "no service" for a few seconds and picks up the m-cell frequently throughout the day but it doesn't seem to affect actual performance. Other than those issues it has been working pretty well with no issues.  It seems to have no problem with other phones, so that may be why some people have better luck.
The problems are enough to seriously consider switching carriers. With low signal at home and almost no signal at work, with m-cell working unreliably, I feel as if I'm wasting money. So come iPhone 5 I'll consider switching to the carrier that has no coverage holes in this county.