I saw that Ubuntu One try to upload 10 files simultaneously and in some moment u1 stopped the uploads:
I changed some configuration values:
simult_transfers.default = 10
write_limit.default = 2097152
read_limit.default = 2097152
on this file:
sudo gedit /etc/xdg/ubuntuone/syncdaemon.conf
by these new values:
simult_transfers.default = 1
write_limit.default = 6097152
read_limit.default = 46097152
I think Ubuntu One works better now with the synchronization.
Did you try this little hack? Please, could you report your result on the comments? Thanks!