I did it for years - the bulk of it was for law firms. I'd love to find the right job again so I can fire my present situation as it is not exactly 9-5 and I have 3 months of hell every year. However, I'm at an odd point in my career, just short of the 10 year mark in administration. I'm totally overqualified for most of what is out there and the rest requires a paralegal certification I don't yet have (and am flaky about pursuing).
My jobs were mostly as Busty described. I spent about 1/3 of my day doing things like word processing, opening the mail, confirming appointments/meetings, greeting clients, and yes - making coffee/picking up drycleaning. The other 2/3 I spent as gatekeeper by phone, editing very lengthy documents, organizing and occasionally leading meetings, overseeing interns/file clerks (most of whom were fucking around on the Internet), and essentially whatever else I was asked to do. Probably the most interesting project I worked on was doing the logistics for an annual stockholder's meeting for a large financial company. That was more project management than anything.
The receptionist gave all of the boss's calls for me aside from lunch hour and my breaks, all of which I often took from my desk. I did a lot of live dictation and both created and worked with forms.
Computer skills, flawless grammar/spelling, fast typing, and a friendly manner with clients whether in person or by phone will transform you from a desk monkey into a secretary.
There is NO.ROOM.WHATSOEVER for ditziness, and if someone came to an interview in any of the clothing posted here, I would probably look at them like they were smoking crack. I like the outfit you picked, Sara, but not for an interview. Bare shoulders and above-the-knee skirts are deal-breakers. Some offices are more casual than others; I've only worked in one that would have allowed something like that and most people that worked there didn't belong in the field at all. Go figure.
You need to be a true right hand person to your supervisor. Anticipate his or her needs. Be creative and proactive and never go over anyone's head. Anticipate the clients' needs as well.
It can be a great job if you work hard, show up on time, and display a consistent level of competence.
My favorite suit is a single-breasted dark gray blazer with a matching knee-length pleated skirt. I wear a plain white dress shirt and sheer or black hose underneath it, moderately heeled comfortable black shoes, minimal jewelry/makeup, neutral nails, and depending on my hair length I would wear it in a simple ponytail or half-up/half-down with a small barrette. Black, gray, navy, beige, or other neutrals are all acceptable. Pantsuits are also fine; some people prefer them. Everything should be spotlessly clean and well-groomed.
Good luck, and ask away if you have any questions.