Running Gwibber 3.4.2 on Ubuntu 12.04.1 with Cinnamon desktop and overlay scrollbars disabled.
Scrolling is really problematic in this version of Gwibber, and I'm not referring to the issues of smoothness reported in bug 828593.
One problem is that as I scroll down, Gwibber often stalls, then erratically jumps, leaving me confused as to which message I was looking at. I'm guessing this is happening because it is fetching data from a database. I'm a bit surprised, though, to see this happen within the most recent 50 or so messages. I would have expected those to be in memory.
Another problem is that the scrollbar barely moves. The scrollbar button is tiny, suggesting the scrolling region must span thousands of messages (30 days worth?). As a result, scrolling around in the most recent 100 to 200 messages causes hardly no visual change on the scrollbar. I can't tell where I am in the list by looking it, and moving it directly jumps in large increments with insufficient precision.
Often when I scroll to the top of the list, either by my mouse scroll wheel, or by sliding the scrollbar button to the top, the scrolling stops, but the top message is not the newest message. It is a screen or two older than the newest message. (I don't recall if this corrects itself after a delay. It could be another artefact of the stalling I mention above.)
Lastly, the scrollbar lacks the up and down buttons.