I've used the N800, Holux M-1000 BT GPS, and Maemo Mapper quite a bit, including in the wilderness on a multi-day backpack trip. I would keep the N800 in the back pocket of my pants and the BT GPS unit in the tent bag at the top of my backpack.

A very satisfactory experience.

I've posted a few places about this, including photos here and some screenshots here.

I've used the same combo several times as a dashboard GPS; it saved my bacon a couple of times on a recent vacation...

EDIT: I've found the Maemo Mapper to be great for routing, including turn-by-turn directions, because I usually know where I'm going before I set off, so I don't need this "offline routing" thing that everyone keeps talking about. As long as I have 5-10 minutes advance notice before we go somewhere, I can quickly grab a route with Maemo Mapper and download the necessary maps while connected to WiFi, and then I'm good to go.

EDIT2: I've had one funny incident regarding this; I stood outside a public library in a small town in the interior of Washington state so I could use their WiFi to grab some local maps for Maemo Mapper, because I wanted to find the easiest way back on the highway...