I tend to prefer doing caching trails rather than picking off odd caches mainly because I like going on nice walks and you get the numbers up of course!
I am going on holiday to Cornwall later in the summer so decided to suss out what geocaching circuits/trails I could do but there was such a lack of circuits. I was assuming they'd be lots, as there are in my area (Oxfordshire), but was disappointed to hardly find any.
I then just discovered the http://geocachetrails.com/index.html website (which is excellant and will come in very handy) and that demonstrates the variation across the country.
There are hardly any in Wales, Scotland, East Anglia and Devon among other places (I realise the site is still work in progress so they may not all be added yet but it seems to accord with skim of the areas). There are a decent enough number of single caches in these places so cachers are there to set them but I wonder why some area have so few circuits?