Google has a lot of untapped niches, and google is on the cusp of a few great things that will throw some pretty heavy weights into the scale.
These are things that facebook is a long ways off of.
Already in motion)
1)Searching Videos and indexing the words/content of the video for contextual searching. They did this with the 2008 presidential stuff and it was in the labs for awhile, seems to have gone quieter now, hard to find info on that. But if google starts indexing videos and being able to search content like that, it will greatly help secure them above yahoo+msn (bing). Imagine them indexing all tv stations and making it searchable, or all Netflix movies etc, any video.
This will create an entirely new niche.
Contextual Video Marketing.
2)Google has another couple of things in the works.
Google Docs this if tuned a lot more it could impact Microsoft office (which is Microsoft’s biggest cash cow), its a ways off but we'll have to wait and see.
[msn/yahoo have nothing in this niche]
3)Android phones are getting really popular and in the new HTC (and probably some older models [i have an HTC so familiar with them]). Don't know if you've played with the "smart search" yet on these, but being able to search relative to your location, restraunts/businesses is addicting.
[msn/yahoo have nothing in this niche that I’m aware of]
Predictions)
I'd expect google to tackle a large social gaming thats entirely cross platform. Tie-in phones/pcs and maybe even playstion (xbox won't do it[thanks MSFT]) on a series of social gaming, all with ability of live video/audio. So you can play cards with aunts and uncles on your phone, on your pc. Even with grandma on her Wii!
Also this would help erode yahoo's market share of their games, which MSN did poorly (think zone).
Next I’d expect that google will attempt to literate the illiterate by putting a heavy advertising campaign on tv that explains how "simple" the new products are to use and that they are free. Furthermore tie-in all web enabled devices ("will be quoted as Standarized devices etc"), so android/pc/iphone/ipad/ipod and possibly ps3.
This will help build the coffin that may eventually contain yahoos market share.
Now with all that in place, it sounds like a pretty good base of content to build an amazing social site.
Facebook did good getting attached with cell phones, tons of users operate from their phone.
But Google could do so much more as a portal/social site.