Since there is no UbuntuOne client for Mac OSX to download, will there be one in the near future?
A Canonical employee responded to that question on the Ubuntu One blog with
in November of 2011. Of course the Ubuntu One client is open source, so anyone interested in helping to make this go faster should contact the Ubuntu One team.
We have released a Mac OS X version as of today. You can find it here:
and check out the announcement here:
There is a project on github that provides limited functionality
EDIT: as Oliviera points out, that link appears to be dead, though the folks over at omgUbuntu are telling us that there is a functional version out there for mac check this out.
EDIT 2: If you are just looking to download/sync files down (not up yet) you can use this python script: https://github.com/ddimmich/unbuntuone-python - this is something I wrote to download music bought off the store.