I've lost a bit of momentum for the 'Things'. Studying, summer and other things beginning with 'S' have somewhat taken over. I'm only 5 things behind, so am going to rush through a bit.
When I'm studying (and generally pootering about online), I'm never at just one computer. Home, work, the UL, the public library - all are different ages and speeds. I didn't look at the other two options as they are not relevant to my current needs as much as CiteULike could be, as that can be accessed from anywhere. I need to have more of a play with it to see if its going to work for me.
I don't know offhand what the students use to keep track of their references where I work, we mostly deal with undergraduates who have a set reading list.