My log and transfer facility seems to have stopped detecting attached devices. First noticed the problem reading the SXS card from my EX3 in the on board card reader on my MacBook Pro, (XDCAM Transfer works fine, btw).
Then tested my home use Sony Camcorder (AVCHD), which always used to populate the list instantly. This time, I was just about to give up waiting after about 5 minutes when the clips appeared.
Finally, I've just bought a Canon EOS 550D and log and transfer doesn't detect it at all. My MacPro doesn't mount it either, although the bundled software does pick it up and can import the clips.
(With the 550D, I have downloaded the L+T plug-in from Canon and adapted it for the 550D).
I had a similar problem once with FCP's Log and Transfer. I never really worked out why but I found that it was only when I was plugged into a network. As soon as the network cable was unplugged, the cards appeared. Weird.
I haven't noticed this problem recently. I'm not sure if it was upgrading Sony's plug-in that made it go away or the upgrade to FCP 7.0.2. You didn't mention what version you are using.
Anyway, if you are plugged into to a network, try disconnecting the LAN cable and see if that fixes it. I can't think of anything else off-hand.