I don't collect Post & Go issues, but I do read about them to keep up with what is happening. Some time ago I got frustrated by the fact that the hobby doesn't seem to know what they are! Some people (including Royal Mail) call them stamps, some call them labels, some call them postage labels, and so on. They are referred to in different ways within the same issue of Gibbons Stamp Monthly.
I decided to do a little investigation. I asked Royal Mail what they considered to be a postage stamp, and I also had some interesting correspondence with Hugh Jefferies, Catalogue Editor for Stanley Gibbons. I also posed the question in the journal of the Great Britain Collectors Club, and I received several interesting replies.
In the end, I decided that collectors, authors and catalog editors each have their own ideas of what makes up a postage stamp. I developed my own definition, and I decided that as far as I'm concerned, Post & Go issues are postage stamps.
Over on the Linn's Stamp News blog, I wrote a brief account of my experiences and I included my criteria for a postage stamp. You can read the blog entry here.
If you have thoughts on the matter, you can enter your comments here or on the Linn's blog.