Subdomain vs Subdirectory for Multisites

Can anyone give me the Google SEO pros and cons for having either a subdomain or subdirectory.

I'm leaning towards subdomains because if there aren't a million links pointing back to my site, there will be less of an issue if some of them are poor quality.

Not sure what else I should consider.

Note: I have a wedding site and will be offering people the opportunity to set up their own wedding sites/blogs on my system.