Having used many remote solutions in the past (based on VNC and on NX), I'm extremely impressed by x2go. Even though it's not properly packaged for Ubuntu (only a Debian repository exists), it worked flawlessly for me in Ubuntu 11.04. Very fast, easy to use, immediately recognized my SSH keys, and even PulseAudio worked immediately with no special modifications.
Best of all, x2go is GPL, making it easy to tweak and embed deeply into the Ubuntu desktop experience. Win win!
One caveat could be that if Ubuntu in the future moves to Wayland instead of X, solutions such as this that are based on X may need to be ported, too. But, assuming Wayland does provide support for X-like environments, it may not be hard to do.