I just bought an MZ-NF610 and yeah, the reception is a bit dodgy, especially deep indoors in buildings, malls, etc. But there are places where I can receive FM stations that were, on my other Sony portables, either too weak or were prone to interference from other stations... A mixed bag. If you need radio with a reliable signal at work, you might be better off getting a separate portable radio instead.
Also, as far as I can tell, there is no mono/stereo setting. The DX/local setting does help sometimes, though. And if there are any other tips for improving reception, I'd love to hear them.