I believe what Rob was experiencing in the Web Garden setup is because of Caching in the application.
With Web Gardens each worker process gets it's own application space, so the cached objects will be different in each one.
This is not really a bad thing. If people are only "reading" your site, then they probably won't notice a page appear in the menu (or maybe disappear), but if you are adding a page, or some other admin task and then you switch to another process that already has a cached object of the TabInfo before the change, you will see "sporadic behavior".
One way around this would be to setup a seperate IIS website using only one worker process that points to your same DNN install and use that for administration.
Of course, if you have high volume updates being made to your site (e.g. forums, news articles) then the sporadic behavior may be more than can be tolerated.
We should probably take a closer look at this and do better cache invalidation, so that processes across application boundaries can stay more in sync.