As someone who is forced to do development and marketing in parallel, I can appreciate the work of a non-technical co-founder. For the record, I am prepared to give equal share to a good marketing person, if only I could find one. Here are some of the few things I'd like such a person to do instead of me, so that I could concentrate on development:
- Market research (as already mentioned here): finding a suitable segment, analyzing competition, studying trends, and so on. This alone could well be a full-time job.
- Non-technical content for the website and social network groups.
- Overall structure of the website (for Saas a website is especially important, right?), including testing and measuring the traffic and user responses on landing pages to optimize the website.
- Maintaining a regular company blog, email list, forum (including moderation), polls, and more.
- Face-to-face marketing: business meetings, meetups, conferences, presentations... Just making a PP slideshow is one big time sinkhole. At early stages face-to-face marketing could be the primary way of getting users, no matter what the product is, and that takes a lot of time. Paul Graham wrote an excellent piece on this: http://www.paulgraham.com/ds.html
- Setting goals and time tables. A developer working without constraints often takes too long to complete the product, because he tends to create a work of art rather than a marketable good. While quality is important too, there has to be a deadline imposed by someone else, or the work will not be done until it's too late. Or maybe that's just me :-)
This list is by no means complete.