Normal modern laptops only have two graphic cards so one can only attach one more monitor. Why not use the phone as a third?
This third monitor can show RSS feeds, chats, email list or updates like for Facebook or Twitter; stuff you might want to keep an eye on but not spend screen space for.
I have back in the very beginning of the millenium had my WindowsCE PDA in the cradle next to the screen where it showed me the email or chat list. Very convenient.
Other stuff it could show is log output, compile/unittest/autobuild results. Let it show memory and CPU usage. Why not keep Spotify or your favourite music player on it.
It should be easy to use it. When I had such a working configuration I had my cradle by the monitor and when I dropped the PDA into it things got connected. (well… it used activesync which is one of the worst programs out there so it didn’t exactly connect every time) Nowadays the cradles are sparse so I only have more futuristic ideas like knocking your cell phone on the monitor and it connects. Or shake it in a certain way before dropping it on the table to let the phone and the computer understand they are companions.
On a side note I today use a small monitor connected through USB. It has worked almost without a glitch. Expensive at around 100€ but, for me, worth it.