Please dont flame for saying this.
The USB startup disk is actually a useless piece of s***.

My experience :
I have used both ubuntu versions 8.10 and 9.04 on usb sticks but sorry to say that 9.04 on usb doesnt last more than 2 sessions.
I had noticed that if u mistakenly access the stick (or just open it) then next time it wont boot up and give whatever errors aka busybox and i/o errors.
But 9.04 is even worse it didnt startup on the very first boot !

I made usb startup disks several times , every time it went kaput after a boot or two ...I tried coz its obviously better than live cd but it was not to be.

Believe me USB startup disk aka ubuntu on usb stick can be the torch holder to end the dominance windows ....only if we can fix it.

P.S: Integration of openoffice has been a great improvement , we should also have integration of codecs.
Most people need just 3 things on their computer : internet browser, Office app, good media player(with codecs).
So if we integrate these three things and make ubuntu usable on usb stick...then may be people would look beyond windows.