Well I guess the first thought that comes to my mind is what content is it and WHOSE content is it, and is it duplicate content.
If it's my blog, with my name on the front door, er - header, or on the About page or whatever, then it's my reputation on the line as to what is being posted. If there are posts on there that I have absolutely no clue what it said - because it was posted automatically from an RSS feed & I haven't even read it - then it could spell trouble.
Even if you check each one before posting, it still could be duplicate content from elsewhere and won't be written in my 'voice' with my thoughts, opinions, recommendations or expertise.
So no - I don't use them.