1. Google size and reach - they already have a huge user base and finally have a viable product (Google Wave/Buzz sucked!) - this is the bulk of the reason they will be 'WINNING' - it's simple - it works - it integrates well
2. Features - ease of use - everything every other social network has and much more user friendly
3. Customization - Privacy settings - Easy to configure - Unlike Facebook
4. Financing - Google has so much cash on hand - they can swallow / incorporate new innovation / talent with ease
5. Less restrictive than twitters 140 character limit and less susceptible to spam bots
Facebook is safe for now because it will be hard to knock them off their pedestal with a 3 year jump start of gathering a user base but they better stay sharp cos' Google+ will come a knockin'
p.s. Ya See cuz Brendan, I'm not such a die-hard Apple FanBoy afterall!