Yep, I got a new Clip+ this week and installed the latest rockbox on it. With my old one I'd been booting to the original firmware whenever I plugged it in, which was annoying in Windows 7 as it meant it'd pop up the crappy sansa window in explorer.
With the new firmware I basically had the problems described in this thread:
I plugged it in from off for the first time in windows 7 and it loaded up the rockbox firmware but driver installation in windows failed.
I then unplugged it and plugged it into a different USB port and it installed the firmware and showed the drives, but they were inaccessible. When I unpluged it, I realised rockbox had hung.
I then shut down and restarted rockbox before plugging it in a third time to a third USB port. It said it was plugged in, but wasn't showing the drives.
I then went into device manager and did a "detect hardware changes" and the drives magically showed up and were accessible.
It now shows up every time I plug it in, even when swiched off, but only after around 30 seconds.
tl;dr turn your clip+ on first, then plug it in and scan for hardware changes and it should fix it