We switched our main University Webmail service (30k users) to Roundcube on Monday:
https://webmail.hermes.cam.ac.uk/
On the whole the deployment has gone well (if we discount a foul up on my part which isn't relevant to this list).
Two issues have arisen:
First a number of people (in particular elderly, important, Professors) have complained about the fonts and colour scheme used by the Larry theme. In particular the fact that there is no way to increase the size of the font.
I don't suppose that plugins exist that would allow people to change the font size?
Failing that do people find that the Classic theme is considered an acceptable alternative? At the moment I have disabled that simply because the Larry theme is a better fit to our new University house style.
Secondly, a number of people report that Firefox (all the reports to date mention Firefox 22 on MacOS, but that may be a red herring) ships with a popup blocker enabled which blocks the "Send" button after a message has been composed:
http://support.mozilla.org/en-US/kb/pop-blocker-settings-exceptions-troubles...
Firefox on my Linux workstation doesn't have any problems, even with the popup blocker enabled.
Slightly more alarmingly we have had one report (and only one report to date) where the Send button only works intermittently, which is harder to blame on a popup blocker. I don't suppose that anyone else on this list has had similar experiences?
For what it is worth: the memcache session storage seems to work just fine on a system of this scale so long as the patch that I submitted a few weeks back is applied (which Thomas Bruederli accepted and has applied as is to the GIT repository).