Hi there,
I absolutely tag social posts - even though GA does show social referrals in the 'Acquisition -- Social' reports, as far as I know, without tagging it's not possible to identify what's owned. I take two steps with links
1. Tag with the following approach to parameters:
utm_source=facebook&utm_medium=social&utm_content=contentname&utm_campaign=socialchannelname-18nov13
Adding the date to the campaign parameter is useful because it can get tricky trying to tie site activity back to a specific post when there's many various campaigns in GA.
2. Shorten with owly - frees up characters in the post / tweet, which is always a good thing.
As for the SEO value - as long as the landing destination has the appropriate 'rel=canonical' tag you should be fine. Implementing a canonical will stop Google passing any value to the campaign tracked URL in the event it gets widely shared, bookmarked, linked to etc.
Hope this helps!
