I've just upgraded to beta 2 of Oneiric/11.10 and the typing break has gone. I've gone into the system settings and looked in "Keyboard Layout" and "Keyboard" and can't find anything. Has it just been dropped? Is there some hidden way to re-enable it?

Update: Thought I'd write an update based on some stuff that has happened since this question (and the two answers) were written. Workrave has now been re-instated in oneiric-backports and for 12.04 (how to enable backports). It works fine, though if you want to put it in your systray then you need to allow it in there. The easy/lazy command line way to allow workrave into the notification area is to do something like:

gsettings set com.canonical.Unity.Panel systray-whitelist "['all']"

But read this question if you want a more detailed explanation about what you're doing here.

Meanwhile the Gnome typing break has been split out into an app called DrWright, however it has not (at time of writing) been packaged for 11.10 (or later).

And as mentioned in the other answer, another option is RSIBreak. It is a KDE app but works fine in Unity.