Just received email... I thought this new change is what the original "changes" were to be... @Linden Lab: make-up my mind, will you please?!
Email from Linden Lab:
Two Important Changes to SL Classified Advertising

Dear SL Advertiser,
We wanted to ensure that you are aware of two big changes to the Classified ad program.
Maturity Changes: Previously, advertisers declared the maturity level of their ads. However, to prepare for teens coming to the main grid, we will be using the maturity system used for Search that is based on two factors:
  • Parcel maturity level
  • Content of the ads themselves
Advertisers’ declared maturity will still be visible in Viewer 2, but will be informational only and not affect the actual maturity rating for each listing. We are targeting these changes for the week of Dec 13th.
Ad Content Limit: All ads have recently been standardized to 256 characters. To maximize relevancy, new characters limits will help you choose only the most relevant descriptive keywords to help Residents find your products and services. Our testing has shown that this limit increased relevancy and click-through rates for classified ads.
For more information, please read about Classifieds on the wiki.
Thanks for advertising!
Kindest Regards,
Linden Advertising Team