Tony

First I do shoot digital images with chroma key green and blue in the form
of rolls of background paperc (they call 'something' blue - Chroma blue
etc - I can;t remember what "something" is but it is a two part name)) I
also have some blue Roscoe paint which is the ultimatte blue (which is
different to Chroma Key Blue but is used in their propriety compositing
system) which I havn't used yet. I don't shoot that much chroma key stuff
that I would call myself a guru. The problem is that some blue (or green)
pixels are left on the boundary and depending on the background you are
pasting over can be seen.

Usually:
the magic tools of photoshop are usually the poorest at cutting out the
blue.

the next best is using channel information in Photoshop to create a mask

the best is a purpose built plugin.

I would recommend to you two books which have some advice on removing
Blue/Green backgrounds (compositing):

Masking and Compositing by Katrin Eisman (a Cs or Cs2 book but the best
of the two for this), and
Adobe Photoshop CS3 for Photographers by Martin Evening

Digital Anarchy have a plugin called Primatte which used to be downloadable
as a test version (full facilities but left their trademark image on the
results). Get a copy and play with it. There are other plugins available
so Google for them.

Regards
Malcolm