Lync vs Jabber
I think the most important thing to look at is how the UC client fits in with the other software users are using more than the phone system or network. If you use Microsoft Office or Office 365, I think there is pretty compelling evidence that Lync is going to be a better choice than Jabber. When I use Lync, I like the ability to choose to either share the entire desktop or a PPT. I like the fact that when I'm using outlook and an email just arrives, I can launch an IM chat with one click.
While another poster mentioned the news of Cisco partnering with Jive, I prefer Yammer over Jive (I've used both for a couple of years each).
With Microsoft announcing plans to integrate Skype with Lync, this is pretty big news that may have impacts for connecting B2B or B2C. I saw an infographic a few weeks ago where in one day alone, 2 Billion minutes of Skype calling is used.
While we don't use Cisco or Microsoft to run our phones today, our IT group announced we'd be moving over to Lync with Polycom phones later this year.