Estimating Projects

I am curious as to which tools and rules do the users of this group apply to estimating for projects in the Americas for the following areas:

Cost estimating & material pricing of piping projects?

Are there resources available other than RS Means or vendor quotes?

Installed cost rules of thumb for example: Weld/Field Cut/Bolt-up cost per size and spec?

Labor Unit rates for Supervisor, Welder, Pipe fitter, Millwright and Laborer.

Do you base your estimates on weight or linear feet? What is the advantage of one over the other?

These questions are rhetorical in nature.