I haven't heard of many nice experiences with Elsevier either, here's hoping they don't mess up such a crucially useful tool.

Well it will surely still work great for managing Elsevier papers.

There will be no favoritism for Elsevier content: http://elsevierconnect.com/elsevier-welcomes-mendeley/

Lots of people have had bad experiences, especially this year. I was one of the people leading the charge against them, in fact. However, they were able to convince me that they really do want us for our openness and they want us to bring that to them. I didn't change my mind easily and I wouldn't expect you to either, all you have to do is consider our track record and continue to hold us up to a exactly the same high standards as before.