Killed the last boss last night...the end credits and the song had me giggling maniacally.
The question I have: other than the fact that Spoiler:
Black Mesa is referenced a couple of times, is there another tie-in to the HL storyline that I missed?
[Edit]
Apparently, they had set up a site beforehand that resembles an old DOS based computer terminal. You can type LOGIN, use any username, and use PORTAL as the password. This will allow you to access an application page (type DIR to see the filename) with some telling questions, and certain letters will sometimes flash to create string that, if you enter it (see spoilers below), will show a camera view and some more backstory. There is also a username and login that you find in-game to access another file that has a timeline of Aperture Science.
It really doesn't do much but add to the backstory, but if you're a story nut like me it's worth a look.
Site:
ApertureScience.com
Spoiler:
login: CJOHNSON
p/w: TIER3
special string: THECAKEISALIE
Application pages: APPLY
Timeline: NOTES