Sounds like something I'd love to try some day. Of course, two days—or even fourteen days—at a single company isn't enough to get much programming done. So I suspect just trying to do normal programming would not really be in the interest of the companies or me.
However, it sounds like a great chance to share some of my more specialized, esoteric knowledge, like functional programming, FRP, verification or synthesis: things which might be useful for a startup or project, but tend to languish away in research labs or deep inside large corporations.
In the future, if I'm ever in a real position to try this—I guess if I get better known and learn more interesting things to share—I'll definitely consider trying something like this.
For example:
* A company looking for a prototype of something that they wouldn't otherwise have the capacity to do
* Refactors
* Code audits
* Four eyes or rapid/agile development partner for a staff member
* Junior dev mentoring/training on a specifc aspect
* Presentation of a technology that might be relevant for which they lack inhouse expertise
* And of course simple app dev. Many inhouse tools can be written in just a few hours.
Edit: Also wondering about the general experience of getting good work done with someone new to the team/project in just a couple days.
We had Jacques, "The Jim Rogers of Tech," (http://www.amazon.com/Adventure-Capitalist-Ultimate-Road-Tri...) for a highly enjoyable two days.
We found him to be intense (on the first day we talked constantly till 9:00 p.m.), wise (he has worked on loads of fascinating projects), trustworthy (he works with many companies at a very high level) and fascinated about everything (he spent five minutes trying to work out how our staircase was made).
We showed Jacques a list of all our challenges and problems, and then for two days we worked through it, asking him for his ideas, resources he knows, etc.. We came away with several pages of useful notes. Since then, he has contacted us several times with further insights he has had.
If you ever get a chance to work with him, I'd highly recommend it.
He was brilliant and very engaging.
Although swombat's account lists his real name, I would never have made the connection. Putting a face on some of the more notorious (in a good way! ;-p) accounts on this site would be .. interesting.
Edit: Whoa, brain is spinning, ideas are mixing. James Altucher (Choose Yourself, author) gives away ideas to network, create value, and ultimately generates business as a result. Something is coming alive in my head. Cool.