I work with pen(cil) and paper from time to time, especially when jotting down new ideas. I like the fact that it feels like you're actually working on something, and for some reason I feel a sense of freedom when working this way. Maybe it's because I'm not tempted to push the play button all the time? I really don't know, but there's definitely a special charm to it. I might start by sketching a few ideas down on paper and then organizing and polishing them in Sibelius, but sometimes I never leave Sibelius, especially if I've been struck by a massive amount of inspiration while being seated in front of the computer.
It's definitely not for everyone, but I would recommend giving it a try to anyone who's never done it before. In the end I guess it all comes down to personal preference. I have never orchestrated anything with pen and paper (I'm not really an experienced orchestrator anyway), but maybe I'll try that someday. I am by no means an experienced composer, so I guess I don't really have a routine yet. Changing methods is a good way to get out of a writer's block though. If I compose something while using an instrument that I'm familiar with I tend to be more set in my routines than when composing with an instrument that I'm not all too familiar with. Another idea could be to compose in a key you're not used to and then transposing it to another key later in the process.
Anyway, I'm getting sidetracked here... What I'm trying to say is that I use pen and paper from time to time and I thoroughly enjoy it.