I was going to ask if you'd set up portrait mode yet, and was then going to direct you to qwerty12's awesome walk-through starting at #38 here (and continuing for several pages), but then it occurs to me that you probably just installed the slide-rotate .deb that's been mentioned, since you have an n810.

In any case, walking through qwerty12's steps was very helpful to me--not only for getting rotation implemented, but also for just feeling like I was getting my hands dirty in ways that the typical end-user might not want to.