Not great. I just got our microcell today. I had it by the router which is no where near a window. It did get a GPS lock when it first started up. But about an hour later it started searching for a GPS signal again and the local 3G stopped working. I bit the bullet and put it in the window on a long ethernet cable that is snaked to the other side of the living room. Shame because it would have been nice if the GPS was sensitive.
I'm sorry to hear that. I actually bought a Microcell a few days after posting that question. I put it on the end of the kitchen counter which is a good 10' from the nearest window, but against an outside wall and it got a GPS lock just fine (this is in a single-level house with a fairly thin roof). We get at least four bars in the entire house (50' square) and all of the back garden (another 30' back) and the front driveway. Given that we had NO coverage before inside the house or in the garden, and only a couple of bars when standing out front, the $150 was absolutely worth it for us.