My two cents...I always give a user the ability to create HTML...but save both the HTML and plain text.

  I almost always end up having to create a search tool for user entered data! When creating abstracts for search results...you just simply cannot count on the returned HTML to be complete...which will cause malformed HTML content results. Using the plain text in your search abstracts prevents malformed HTML in your page displaying the search results...but when a user clicks on a returned link, you can now provide them with the full HTML content.