I've been lucky enough to get my hands on a Magellan eXplorist 710 GPS and have been using it for about 3 weeks for geocaching. This series is newly launched in the UK and I've written a detailed review of the 710 with emphasis on geocaching to help people understand more about it and the features available.
The 710 is the same as the 610 and 510 but with some hardware differences (compass, camera etc) and pre-loaded maps available.
The review is a pdf document, to download it click here.
Chris