I recently got a Dell ultrabook and was trying to install Ubuntu on it.
I was able to successfully download the .iso file onto my USB drive using Universal-USB-installer, and was then able to load the Ubuntu installer.
However, when I chose the option to "install Windows 7 and Ubuntu side-by-side", the computer restarted and then opened up Windows instead of continuing to install Ubuntu.
Then, I tried to change the order in which my computer chooses to boot...booting from the hard drive was ahead of booting from a USB drive, so I switched that. Then I tried to install Ubuntu again, and the the same thing happened...I chose "install Windows 7 and Ubuntu side-by-side" and the computer restarted, and instead of continuing to install Ubuntu, I got prompted to begin the Ubuntu installation process (or to "try" Ubuntu).
Also, I tried to the "Windows installer" by downloading wubi.exe that was supposed to be quick and easy...but then I was only allowed to choose a 30 GB installation size (the partition that Windows is on has currently 92.95 GB with 65.21 GB in Free Space, according to Windows' Computer Management). I'd like more than 30 GB on Ubuntu, and I don't see why it's not allowing me to choose more than 30GB...