You could probably add Picasa, Reader, Virtual Voicemail / Google Voice, Calendar, Video Chat, Instant Messaging as well.

Yeah, though they haven't really dominated any of those sections - I considered a few, actually. Picasa for instance is decent and moderately used, but Flickr and especially Facebook are way way larger in almost every respect.

Their calendar is the best online calendar I've found, but nobody I know uses it except Google-aware geeks and the ones I've taught (they love it now, didn't know it existed before). And online calendars haven't really reached public-awareness or usefulness yet, it seems - the closest most people come to computer calendars is their work's shared calendar that runs through Outlook.

Instant messaging they've certainly impacted, but I think AIM and MSN and Yahoo individually still out-number Google, though that may change with Plus. And Skype dominates video and voice chats, though Google is a threat (again, depends on how Plus pans out).

edit: Though Voice is incredibly awesome and absolutely dominates in its niche - of course, it's the only contender. But nobody knows how to use it, and its user-base consists of a laughable amount compared to <random national telecom>, AFAIK.

Agreed that the market penetration is still limited for many or most of those things, but I imagine Google's offering has made a disruptive splash to more than a few companies.

Yeah, we agree there :) I, for one, like the disruption - even if Google doesn't do it better, it spurs changes.