I reblogged that last post just because I wanted to know what it was like to do it. 

The biggest problem I see is that people may think this is my content.  The source is tucked away at the end of the post and is hardly noticeable.  How about after the title “Social Blogging” have a dash and then: “From XXXXXXX Blog” or Social Blogging - “From (URL HERE)”

Another option I can see working is before the title of the post put “Reblogged - TITLE”

Anyone who casually reads my tumblr could easily make this mistake.