In 'Making Pictures Better' Sunlight has written a very good and explanatory piece on Black and White Photography and the need to consider the tones in an image. It is here

http://www.myfinepix.com/forum/33538/365071

and whether you are shooting in B&W or converting to B&W there is always a great deal to consider. To try and show the need for seeing in B&W I have converted two photos - one with few variations in tonal variations and the other with many more.

As you can see even in colour the sparrowhawk is fairly well camouflaged and the tones are very similar. A straight conversion using Photoshops B&W makes that similarity even more difficult to see the Sparrowhawk,

Even using dedicated software for conversion does not make the situation any better - different but not better.

EDIT As an addendum I thought a photo converted to B&W using the Channel mixer option (as suggested by jevoncarey in the comments on Sunlight's Photo Feature) would be useful to see.

which is in my opinion no better (or worse). Again it is different but it is the wrong sort of picture to be converted.

Whereas using a photo with a wider variety of tonal variations which can be used to make more distinctions and create a more pleasing image.

This converts to

This was using dedicated software for the transformation but a straight transformation in CS4 is far more satisfactory as the detail is clear.

EDIT

And again using the Lab colour/channel mixer conversion.

Hopefully this will give some idea of what should be converted and the best conversion method and demonstrates some of the problems when converting to B&W and gives some suggestions about the sort of photo which works well.