Small startups: do you ever wish for a QA contractor to work one day a week?

I'm an experienced dev and tester with 10+ years of experience under my belt. I've worked at both successful and failed startups, big corporate, and small agency. I'm really good at finding bugs and identifying their causes. I can also point out potential issues with the UI and usage flow. I know how to communicate with developers, users, clients, and project managers.

Do you ever wish for someone to log in or come in once a week or for an hour a day and kick the tires or put your app through its paces? Have you actually found someone like that? If so, how? What does your contract look like?

Do you think this type of service is useful or just a pipe dream?