I've been doing well from my horoscope blog in the signature lately and I'm hoping it doesn't get flagged because of the ad positionings which are bang in the middle but as far as I know it's not against Google's terms and conditions. It has lots of content, so can it be classified as a MFA site when it's not, simply because the ads are the first thing a visitor sees on a page ?
That won't be a problem. You have an aggressive ad layout, sure, but there is lots of content, so no problem with it being mistaken as an MFA.
I think an MFA site is when a site or blog posts it content automaticaly, like it posts content from RSS feeds or Yahoo groups.
I have ads positioned directly at the top of each post on my blog websites and have never once worried that Google would consider my websites as MFA. I'm confident that provided you actually have decent, unique content on your website then you will be fine.
Your blog have content is uniquely and look not like MFA. The ads are the first thing a visitor sees on a page is Great position.