Yes, I've done it, as have many of my clients. My advice is that if you can't afford to do it well, don't do it at all. A good, effective television ad costs a lot to produce and run (compared to other mediums). So does a bad one.
If you're advertising a product or service, it's essential to have a clear selling point, professional production, selective scheduling, saturation (multiple ads when your target audience is watching), and continuity (ads running steadily over a period months). Consequently, you need to be able to afford all that up front and keep it going for a long term campaign. Your product or service probably needs to sell with a high margin to make that kind of television advertising cost-effective.
If you're advertising an event (like a show or sale), that can be done with less elaborate production and an ROA schedule. You still need saturation, but only for a few weeks prior to the event. It's a much easier and more affordable type of campaign for most small enterprises to budget for.
Your profile indicates that you're in the restaurant business. Most long-running ads for local restaurants are boring (says market research, not me), so taking an "event" approach would not only be less expensive, it would probably be more engaging and effective. (For example, a Mexican food restaurant in my area that doesn't normally advertise ran very effective Cinco de Mayo campaign, figuring that if they draw new customers in once, they'd keep some of them as regulars.)
Check to see if your local cable operator can do "zoning" -- where your ad only runs in the neighborhoods from which your customers would come. That can be a real cost saver for businesses that draw from limited geographic areas.
Also bear in mind that this fall, political ads will be dominant. If you have races in your locale that are being hotly contested and political campaigns start buying up the available airtime, you may suddenly find that it's impossible (or much more expensive than you are being told now) to get ad slots. If I owned a small business that had never done television advertising before, and was considering a long-running spot (as opposed to an event type ad), I'd be planning and budgeting now for a campaign that would launch in January 2009 (after the election and holidays).
Hope this helps. Best wishes.