An update on Guernsey mapping for you - the last OS map was done in 1983 and is out of print. Specialist map shops may have a copy. It's set on UTM zone 30 datum, and I have successfully set my Vista HCX to use that datum. There have been many new housing estates built since the map was produced, but all the caches are in areas where there has been little or no development, so you'll be fine.
In more recent years the Government (States of Guernsey) have created a 100% GPS-created map of the island - see www.digimap.gg for more details. This is available as an OS-style 1:25k paper map from them by mail order, or in local shops. The problem with it is that it's marked with grid squares for the 'new Guernsey grid' which GPS devices can't handle due to the origin not being on the equator. It does have the UTM grid marked on the edges, so with a pencil & ruler you can plot your cache locations with enough accuracy to get to the nearest carpark. It is being re-released later this year, possibly at 1:15k scale.
With regard to the important question of real ale & cider The best pub for that is 'The Cock & Bull' at the top of Cornet street - lots of CAMRA awards. Other good pubs are in the CAMRA good beer guide. There is an award-winning local brewery, the Guernsey Brewery.
Although I'm new to caching I have a very good knowledge of the island and am looking forward to placing a good few caches of my own in time for tourist season - if any visitors want to place caches then I may well be up for doing maintainer duties.
