I am honestly not 100% sure and would love to hear an answer from some AOL users on this...
...but when I published Self-Starters Weekly Tips in html format I would get replies from AOL users, WebTV users and ocassionally a few others that they got a garbled version of my newsletter and were unable to read it.
With a growing list, and a large number of these types of users (being that newbies & "self-starters" usually start with one of these types of ISP's)... I switched to plain text.
I also found that my formatting would come out odd in hotmail & yahoo accounts - not necessarily "garbled" but not neat & clean like it came to me in Outlook.
Keeping in mind that everyone's email box is different, as well as their screen size & resolution... its also important not to format specifically for YOUR screen width when writing your newsletter... as this will cause funky line breaks in smaller screens or lower resolutions (learned my lesson on that one too! LOL)
Hope that helps
Anyone else??