I want a personal assistant for 5-10 hours a week. Not a virtual one because most of the things I want done are in meat space. Stuff like filling out forms, doing my laundry, waiting in line for me at the DMV, and dropping off my netflix returns in the mail. It sounds petty, but I really hate running errands and filling out forms. I'm considering hiring someone off craigslist.
I've often wanted the same. The main problem seems to be that it is probably hard to make a living as a personal assistant at the prices you and I are willing to pay. There is also the trust issue: would you really trust a stranger enough to do sensitive things?
It just so happened that the previous day when my girlfriend asked me what I wanted for my birthday, I gave her a list of errands to run, people to call, and forms to fill out. She says I should just pay her instead of hiring someone, since she admittedly does do a lot of this crap for me anyways, but something doesn't feel right about hiring my girlfriend to be my personal assistant.
Regarding the business side of things, it might be feasible if you had a central service that could distribute the load of multiple clients among a stable of assistants. You sign up for X hours per week, and you get an assistant on retainer. Maybe you pay a premium if you prefer to work with one person exclusively. Locality could be a problem though, because you would ideally want your assistant to be pretty close to where you work/live.