It's BBXiong

S4
HTC One
Z

or

BB10

or...

wait and see how on
Sailfish

Social Integration directly to Inbox and Sharing on Gallery to Social Network was done on Maemo.
What's new on MeeGo is the Events View which shows all your social network feeds, RSS feeds, etc. but there's still a lot of room for improvements for this. WP implement similar but a lot better and detailed.

I'm not sure how much difference in terms of flexibility between MeeGo and Maemo, but for Maemo, you can add plugins by 3rd party for additional integration.
e.g. By default we have few social networks integrated into Maemo (later FB was added "officially")
For 3rd party, we have so many to choose from, MSN, ICQ, etc.
But MeeGo, I didn't seem to see we have such options.

N9 would be more nice as a phone, but I still prefer the N900 as I always looking for a true proper smartphone. The reason smartphone were created last time was beacuse there was Pocket PC and a phone, people have to carry 2 devices. A smartphone should be a Pocket PC (pocketable PC, mini PC) combine with a phone, but thanks to iPhone, the trend changed.

Anyway, N9 and N900 both have pros and cons.
N900 is a more proper OS, with cool and proper Desktop where you can place icons, widgets FREELY (even overlap) just like your Windows Desktop, it's nothing like typical smartphone Homescreen. You have better web browser which can render better Desktop webpage, you can activate mouse cursor and do a right-click and the support of Stylus is another plus. Overall, it brings you closer to the feeling of having a mini computer in your hands... and finally, the qwerty keyboard. oh, still the best qwerty around, select-all, copy, cut, moving cursors, it's just so good.
N9 on the other hand, you will feel more like a OS made for phone, emphasize on simplicity but yet it's still very capable. It's nicer to use as a phone, and the swipe and double tap to wake is really a nice innovation.
Personally, N9 is not a proper replacement. It more like depends on what you want and need, just like back then you have Nokia Communicator which caters for people who like these types of phones, while N9 is more toward normal smartphone users.