I have two Win 7 machines and two Ubuntu One accounts.
-- Windows 7 Home Premium runs Ubuntu One client fine.
-- Windows 7 Ultimate will install it, but the client won't open. I've let the 'getting information' screen run for 45 mins.
A previous answer to a similar question suggests abandoning Ubuntu One for Win 7 as it's 'too buggy'. Any other suggestions? In the meantime, I'm off to try other offerings. Shame, as I liked using Ubuntu One.