Do Subdomains Pass Off Juice To The Main Domain
 

i know the common wisdom is that subdomains are treated as separate domains, but would links built to say mobile.yourdomain.com and forum.yourdomain.com help the ranking of your main domain?

also would the benefits of high pages views, activity and low bounce rate on a subdomain be passed on to your main domain? any experience?

good question.

They must, look at tumblr for instance.

Use canonical tags.

Not knowing the answer myself, I just set up those things as a directory on the domain and then subdomains that forward to the directory.

The short answer, yes :) Treat them as you would a separate domain. Obviously the amount of juice your separate subdomains have the more juice they'll be pushing to any links; regardless of whether the links are to your own subdomain, separate domain, or a third party domain.

WTF?!

Whatever you do, do NOT use canonical tags... that's how you tell the search engine it's duplicate content... I doubt that's what you're trying to accomplish.