Two polls about sleeping habits. They are not quite orthogonal, they could be combined to one if you really want to; or some options can be removed if you want a shorter poll.

I usually sleep ...

• lying on my back
• lying on my front
• lying on my left side
• lying on my right side
• lying curled up on my side
• lying on either my front or my back
• lying on either side
• lying in any position
• sitting
• standing
• walking
• I never sleep

I mostly sleep ...

• on a bed with a soft mattress
• on a bed with a firm mattress
• on a sofabed
• on a foldable camping bed
• on a hammock
• in an armchair
• on a mattress on the floor
• on the floor
• in a tent
• outdoor in a sleeping bag
• on the street
• sitting on a vehicle
• over work/studies
• in a meeting/conference
• walking
• (Update) via 4-arg select
• I never sleep
• I always sleep

(It might also be possible to ask about what kind of pillow one uses.)

(Update: thanks for ysth for his suggestion.)

Update 2008 sep 6: second one done: I mostly sleep...