On our website, for each short story (and in the table of contents for the ezine), I list the word count first, followed by an estimated number of pages.

You'd be surprised how many people (especially avid readers) can guestimate how long something is by the word count. They may not know exactly how many pages "10,000 words" is, but they'll recognize it as a short story, 100,000 words as a short novel, and 300,000 words as a long novel.

I haven't had any feedback (positive or negative) on using the word count & page count numbers, so I can't really say how effective it is from a customer's perspective.