We travelled North on the Fort William portion of the Highland sleeper last summer. Service was fantastic - we'd been advised to be prepared to move our cycles from the Aberdeen (I think) brake van to the Fort William brake van when the latter was added at Edinburgh, but the steward took it all in hand and moved them across for us (making sure that we didn't lock them in any way!).
I struggled to get any meaningful sleep myself (maybe I'd sleep easier on a second or third trip). The aircon didn't help - by the time I'd got used to the continual drone, we'd run through a neutral section, the aircon would shut off, I'd wake up, and the whole cycle would start again. Funnily enough, as soon as the 67 came on at Edinburgh, I slept soundly for a good couple of hours - whether that was because the aircon was running continuously after that, or whether it was the noises from the front that sent me to sleep, I'll never know!
The berths aren't the most spacious, but there's still room to do what you need to do. I wouldn't like to be sharing a berth with a stranger though, especially with a couple of decent-sized bags to find a home for too.
Quite a nice sight upon arrival at Fort William, with the kettle on the Jacobite waiting on one platform, and our 67 on the blocks on the other - and not a unit in sight!