What are good ways to deal with an area that needs temporary floor covering?
I'm going with paint.

Research elsewhere on the net found some interesting stories about people putting down a new floor after a P&amp;S floor.  Getting the old tiles up, and removing the glue was a serious PITA, right up there with older style glue down floors.

So...

A "Temporary" floor should be done in such a way that it is easy to remove, or can be covered over when comes the time to replace it.  To that end I rate the following as reasonable temp floor solutions:

Do nothing


Very cheap and quick.


Downsides:


Chipboard isn't a good wear surface, nor is is good with water.
Tacky looking.  You see all the work stains paint drips, etc from the construction time of the house, plus whatever got through the previous floor covering.


Paint it.


It keeps the dust down 
It gives a smoother finish.
Prep work done for painting would likely need to be done for a permanent floor too.
Gives some protection against wear and water damage.


Downsides:


Block access to floor while painting.
Needs at least two coats for any kind of durability.
Looks cheap.
Not easy to keep clean.


Paint could be augmented with some form of filler first to make it smoother.

If the floor is a the really cheap sawdust board, there is merit in using a non-waterbase primer.

Also:  If you can, use recycled paint.  No point in using expensive paint for this.  

Carpet Runner / area carpets


Really quick to put in.
less tacky looking than paint.


Downsides


More expensive
Cheap area rugs may not stay flat.


A variation on a theme:  If you can access used carpet, cut a chunk to fit, and as a temp covering, staple it in place.

Another variation:  If your area run doesn't do the whole area, paint first, then the area run.

Laminate flooring &amp; Vinyl Plank flooring.

This is close to a permanent solution, but for a temp solution you may want to use whatever is cheapest at The Orange Box, and take shortcuts in the installation, such as duct tape transition strips, and being less attentive to detailing.  May make sense if the temp area is small compared to the entire area you will be doing.

Loose lay vinyl.

Another more permanent temporary solution.  This is a form of vinyl flooring stiff enough to just lay on the floor.  I've used it in a bathroom 12 years ago, and it has worked well for me.  But even cheap vinyl can be stapled in place.

This is, I think, the best solution for a bathroom, especially if the existing subfloor is one that can be easily water damaged.