Switching from Ubuntu 11.04 on your HP to Mac/OSX will add the following:

- ability to use applications only available to Mac/Windows (like Netflix, Office)

- can buy/use Textmate

- a smoother GUI to work/play in

- the religious euphoria that comes with using iStuff

Ubuntu is working hard to improve the UI and have things "just work" but it's still lacking general adoption as a third pc/user platform. My laptop is on 11.04 but desktop is still Windows7 (+ 11.04 in Virtualbox) for that reason.