I have an IBM Thinkpad with no serial port. For downloading from an
LX-5000, I have used a Belkin USB to serial adapter. It has worked fine.

I now am trying to download from a Cambridge 302. When everything
works, it takes roughly a minute to download 3 minutes of flight data
(and at least a minute just to change the name of the pilot). When
everything doesn't work (about half of the time), you have to
reinstall the Belkin software before you can establish another
connection.

Apparently, you aren't using an Ipaq with the 302? If you have one, it
will download the file - doesn't solve the laptop problem, but might be
more convenient.

Yes, it seems that is the way to go. After downloading to the Ipaq, I
can transfer from the Ipaq to the laptop's USB port, and so avoid the
serial-to-USB problem. It adds an extra step, but should work.