Text Ads or Banner Ads (not affiliates, but locally sold)

Do you have a question? Post it now! No Registration Necessary.  Now with pictures!

My site currently sells graphic banner ads to local businesses, at a
flat monthly rate. These are typically 120x120, with 3 shown on a page
(chosen at random with each page refresh).

There are several problems with it, though:

1. A lot of small businesses don't even have a logo, so it's not
uncommon for me to have to create the ads completely from scratch,
with little or nothing to go on.

2. Other businesses think that they can have me fit long sentences in
a small 120x120 box.

3. It's not entirely uncommon for me to build an ad, send it for
approval, then simply never hear back from them. That's a lot of work
and time invested for nothing!

4. It's also not uncommon for the business to cancel after a month or
two, which makes it questionable on whether that was time well spent.

5. It's really just me building the ads, but I have other jobs to do,
too. So sometimes, new advertisers get pushed to the back-burner when
I'm working on bigger projects, which is really very unprofessional.

Because of this, I'm thinking about changing the ads over to 120x120
text blocks that the visitor can create themselves (using a
contenteditable field), select how many days they want to run it (so
they could potentially advertise for 1 days, instead of a full month),
then pay immediately. At that point, the ad would be emailed to me for
approval, and all I would have to do is click an "Approve" button.

Here's what I'm wondering. Have any of you guys gone through a
transition like this, and if so, was it received positively or
negatively by the advertisers?

Site Timeline