As a houseguest, how much tidying up do you need to do before you leave? I was just looking around on the internet, and one site said to strip your bed, stuff the linens into a pillowcase, and leave it all at the foot of the bed. Really? Then your host has to pull all that back out of the pillowcase in order to stick it into the washer. Should I come downstairs with an armful of sheets? Should I ask for the vacuum so I can suck up every last stray hair in the guest bathroom?
If my host is a total clean freak I feel like I need to erase all signs of my presence, but I also don't want to seem like a weirdo by overdoing it. Last time I stayed with someone I surreptitiously grabbed the dust buster when she was out and did some cleaning, then I wiped off the counters and the mirror in the bathroom, got rid of the bathroom trash, inspected the shower, and shoved all of our towels into the washer. I made the bed but didn't strip it. I think my most egregious offense was my child left a dish on the table, but we both had come down with wretched colds and just wanted to get out ASAP. Was I a terrible guest? (I can't help we got sick. That's life.)
I think even a clean freak would be freaked out to know you were dust bustering their home on the q.t. If you are staying with someone for an extended period of time, say, more than a week, ask how you can pitch in with housekeeping. For anything less, my rule of thumb is to keep sleeping quarters tidy, confine your belongings to the guest room (or a corner if you're sleeping on a pull-out sofa) and clean up any messes that you directly cause (juice spilled on the counter, for example).
As far as whether to strip the bed at the conclusion of your stay, if you know your host well enough to stay in their home, you know them well enough to simply ask their preference. Phrasing like "I was planning to strip the bed before I leave, is that okay?" lets them know you're happy to do it, but lets them politely decline if they prefer to do it themselves.