I've had the same problem with my Xoom from day one (March 2011). I've
read some solutions but they were exceedingly complicated and the one
that worked didn't succeed in the second machine I tried it on.

I think there is a need for something to be added to (K)ubuntu to make
the Xoom connect. I don't know any more than that but I sure wish some
member of the community would figure it out and make it available. If
it works on Windows there is no reason I know of why it can't be made
to work on Ubuntu... please!

I can connect in the other direction, over the USB cable, using a File
Manager on the Xoom, but connecting using the PC would be a bit easier
(full size keyboard, big monitor etc.).