I'm about to press in a PF30 BB, and I was curious if it is recommended to lube it before pressing in?  I would think so, as it would reduce the possible creaking, but I would not want to introduce the ability for it to slip.

Always use some form of lube if your working with Alum-to-Alum or steel.

I would not consider WD-40 a lube. But better than nothing.

Just plain oil, Lithium grease or Sunnen brand makes a actual lube for press fitting.

As the letters state "PF = press fit" so there should be no slippage issues if the press

sizes are correct.

My recommended steps:

Inspect the parts for machining burrs or excess coating or paint. 

I like to Scotch Brite to clean the surfaces and improve finish.
I'm not really changing the size of the parts.

1) measure the frame and the bushing your pressing before installing.
(make sure they are the same temp when measuring. Don't have one part in the 
air cond. house and one part out in the 90 degree shop. Do those measurements meet the manufacturers specs???????????

2) In the racing engine business we will typically heat one part and freeze or cool the other. Makes pressing much easier.

3)I'm not apposed to using Loctite-green bushing locker if the press is not as
Tight as recommended or for extra security. In that case don't cool or heat anything.
Just press it together

Sorry if this old news to you.

Best wishes
Todd