1. Writing the copy for the website. Mainly keeping the support documents up-to-date.
2. Doing all the business related tasks.
3. Doing all the customer service.
4. Handling all incoming e-mail.
5. Doing all of the social networking stuff (facebook, twitter).
6. Doing all of our marketing. Handling Google AdWords, banner advertising, text advertising, etc.
7. Dealing exclusively with our accountant.
8. Tracking all of our expenses, etc., into Excel and getting everything ready for accountant (see 7).
9. Handling all legal work with our lawyer.
10. Doing all of our networking. I'm the guy that goes to all of our relevant events.
11. We all come up with ideas for product development.
12. Blogging. I do all the blogging.
13. Handling payroll. I do that.
14. Dealing with the bank accounts. I deal directly with the small business rep at our bank.
15. Market research. I find out as much as I can about our competitors, what they do, etc. I also learn about our market as a whole.
16. Handling all incoming advertising requests, setting up their campaigns, etc.
17. Dealing directly with all our merchants (credit cards + PayPal). Dealing with the very few chargebacks we receive.
18. Paying all of our bills (server expenses, software licenses, domains, advertising, etc.) and monitoring our cash flow.
19. Pitching. I handle all of that.
20. Anything that requires a phone call. Incoming or outgoing.
...and many other tasks as they crop up. For example, I'm the point person on setting up our new office.
My job is a lot more "flexible" so I can deal with things as they arise and take the lead. Whereas my partners (one is a designer and one is a coder) usually have to stay on task so they're not distracted. For example, we're setting up a new office as I mentioned above and it's just not feasible for either to spend time dealing with that in the middle of production. I, however, can do that.