I picked up a Garmin Dakota 20 a couple of days ago.
For me the key features are:
- Small size - you can carry it in the palm of you hand or fit in your pocket.
- Ability to use micro-SD cards
- Ability to load multiple mapsets - no longer constrained to the gmapsupp.img and the few alternates available
- Sensitive receiver - quick fixes and ability to maintain a lock in tricky conditions
At this early stage, I've not come on many negative points, the only one would be the tracklog recording system is not as straight-forward as recording tracklogs on my 60Cx where you get a nice unique .gpx file named with the date. The Dakota (and it's Oregon sibling) automatically archive (when the tracklog reaches 10,000 points) tracklogs into file names 1.gpx through to 20.gpx and then start overwriting the files again from the start. Each 'automatic' archive contains 5,000 trackpoints... a total capacity of 100,000 points if my maths works out.
Clearly you will need to manually archive tracks on trips if you want to keep them. You are able to archive up to 200 tracks, and they loose none of their detail unlike older GPS units which strip out quite a bit of detail.
On the subject of tracklogs, I found the altitude in recorded tracklogs pretty erratic, so I changed from barometric altitude to fixed altitude (GPS derived). Setup | Altimeter | Barometer Mode | Fixed elevation.
New system software allows georeferenced images to be used on the GPS, useful for areas where Garmin format maps are not available. I've experimented a bit and would only use georeferenced images as a last resort