A couple of weeks ago I gave a lecture on library resources to about 20 fourth-year students. Included in the show-and-tell was our new libguide-based subject guide, and my new meebo widget. I took the opportunity to ask, "So you can contact me by phone, email, meebo, or face-to-face. Which do you think you'd be most likely to use?"
The responses were: email or face-to-face. A bit disappointing (after I'd spent some time explaining to colleagues and managers the advantages of the meebo widget) but interesting.
But. That was Friday. On Monday I got a Meebo query, and on Tuesday I got another Meebo query. So even though the class had said they would use some other method to contact me, 10% of them, while browsing the subject guide, saw that I was online and thought they'd contact me that way after all.
I officially approve of asking users what they think about things - but it's not perfect. The only way to be sure whether something's useful or not is to try it out (and market it!)
[Obligatory acknowledgement that we can't try out and market everything. But we were already using a meebo room for online reference, so adding a widget to my libguides took me less than 10 minutes.]