I think in both cases it was less hack and more getting around browser sniffing code that makes outdated or incorrect assumptions.

Please don't browser-sniff, use feature detection instead. The web platform is standards-driven, not browser-driven -- let's keep it that way :)

I'm sympathetic to the need to do this, just admiring the kludges. It's not just user agent spoofing; some of the compatibility hacks seem to be modifying CSS of websites.