Yes, exactly that. It just appears as another disk drive, like a usb stick. I had an Etrex H, which I was generally very pleased with. However, it suffered from a bug, where it would shut down for no reason every so often.
I am writing an article about using GPS units and plotting tracks on maps, etc for a computer mag. I used some of the money to buy the E20. I have only had it for about a week, but so far I am very happy with it.
I have uploaded the OpenStreetMap image for the UK to the E20. I have found this works really well and it's free. I am more interested in using the Etrex to record my tracks and getting an OS grid ref. However, I find that using the maps on the eTrex enables me to see where I am at a glance. Most of the time this saves me having to get out the "proper" map to check it against the grid ref. This proved very useful on my last trip in clag and driving rain. Not the sort of conditions you want to be trying to read a paper map.