What should I look for if I am to invest in Nordic walking poles? Any recommendations / issues I should be aware of?
I have a pair of Leki poles that I really like, but they are really expensive and I am not sure that others aren't basically the same for cheaper. Mine have lasted since summer '00 and are still fine though.
Working from the top down:
First you want ones that have easily adjustable straps at the wrists, because they help distribute weight.
The grip sould be a neutral position. I really don't like the ones with the little handle on top, I feel it gets in the way, but ymmv on this aspect. I also don't like gummy grips. But that is all personal opinion.

Mine have three sections, so they are really small when they are folded (well not folded, but the sections fit into each other). I like it because they can fit in my duffel bag for travelling on airplanes, but this can be a point of failure. The more sections you have the more likely a pole will loosen and slide together.
While hiking you are supposed to have shorter lengths for uphills and longer for downs. The only place I really used this was in the Whites, but you might like to use it more often so make sure you find changing the length of poles easy. Some have like little clips, mine just twist.
Anti-Shock or not?
I have anti-shock. I really like it, but my friend hates. It has a little spring inside and I think it helps, but also provides me with amusement while sitting around. If you get poles with anti-shock make sure it can be turned off by twisting the poles into locking position.
What type of tip and basket does it come with?
This is the only thing I find annoying, my pair of poles did not come with a rubber tip to put over the metal end, not a problem when hiking on grass covered areas, but an issue with rocks.
You can buy tips and baskets as extras, but I always forget until I am headed over the next set of rocks.
I suppose the other thing is the material of the poles? I can't imagine anyone using anything other than aluminium these days, but I am sure some cheap-os might.
These are my poles.
http://www.leki.com/trekking/trekkingPole.php?pID=42If you like taking pictures some poles come with a built in camera mount as well.