On this system (Win 7, 8 GB RAM) with Firefox 18.0.2 I see that missing text effect even on reload.
In Firebug that Google returns a 304 for the Ubuntu font files but the browser is requesting the only about 3 s into loading the page. Really irritating.
I can understand the desire for a nice menu or heading font but the whole website?
Here's that page:
http://portableapps.com/apps/development/notepadpp_portable
Looks like it uses Ubuntu font-face for everything. It's a nice font but Arial would have been fine too.
Also looks like the font is hosted on a third party site googleusercontent.com so I guess they are hoping you've cached it before.