Knitting needles

I'm thinking of picking up a set of knitpicks interchangeables. If I do, I'm wondering:

Nickel plated vs. Birch wood  --  fight!

I'm also wondering how these options in your opinion compare to plastic or bamboo?

Another knitting question

How often, honestly, do you end up using really small needles (US 0-3/Metric 2-3.25mm)? How about specifically US 4/Metric 3.5mm?