I promised myself I wouldn't install 10.04 until it was released, but seeing news of the release of beta 1 splashed everywhere changed my mind.
My response having installed it was something like...OMG WOW!!!!!!!!
I am truly amazed, I'm going to go all American and even say it's "awesome". It looks fairly decent out of the box (borrowing more than a few looks from OS X) but it's also extremely fast and very stable (especially for a beta release!).
I like it that much I gave it a whirl on the MBP too, and was surprised to see that almost everything worked out of the box! A few proprietary drivers and a few tweaks later I had everything working except the sound - which is a shame, because if the sound worked I was fully prepared to kill OS X in favour of Ubuntu (although I'd need a new solution then for syncing my iPod Touch).
All in all I heartily recommend it, if there was ever a time to install Ubuntu on your mother's computer the time is now (or April 29th if you're more cautious
).