Proxies with link building?

I rarely see talk about IP addresses with link building.

How necessary are they?
Do I need to be careful with anything else then IP, browser versions and creation dates?

How much can you build with one proxy? Can you register into 10 different video, article or document sharing sites and link from there?

I'm just starting SEO and feel like you have to be super technical when playing chess with a super machine like Google.

Answers are appreciated.

If You Are Using Diffrent Sites Then 1 Proxy Works Good And If You Doing Multipal Projects With Repeated Sites Then Try To Use Random Proxies For Sites!

You should be really careful about IP addresses, proxy etc. One account - one proxy, do not mix them! It is also important to have a strategy and a plan with the quantity of links per day/week and do not build too many links at a time.

I'd prefer using some link building service that offers links from different C-Class IPs.