I'm not a software developer (researcher), but are there really no tasks simple enough for interns in your average software company? When I worked as a sysadmin for a couple of months, the two (paid) intern programmers seemed to do most of the work on some (small) contracts. They definitely had some things to learn, but they got it done (with some help) and were absolutely net positive.
Maybe we just had unusually good interns, though (this was in the Netherlands).
Tasks that simple don't provide them any experience and we're back to paying them for work done.
Complicated tasks need guidance and take time. But they're great for experience.
It's not even that they're really hard tasks, but that there are so many little details to software develop that everyone treats like common sense, but it's not... Until you have experience.
In this specific case, they created some simple Rails websites - one seems to have basically been a simple CMS (with a nice design) for a customer, another was an internal time tracking tool. Both had at least one (more-or-less harmless) WTF [1], but the customer seems to have been happy, time tracking worked, and they definitely learned something.
[1] To be fair, one was putting my sample code in production.
Maybe we just had unusually good interns, though (this was in the Netherlands).