I am using OpenCPN, which I found easier to use than SeaClear. Installation, adding maps, etc seemed very intuitive. The program is free, open source and available for Windows and some Linux flavors. I think they are working on an Apple Mac version now.
There is reportedly a bug when using OpenCPN on a Windows 7 64-bit system (which is what I am running). The program runs fine, but would not recognize the USB GPS. It worked fine on my Windows XP machine, but not on my Win 7 64-bit.
I found this program ($12) that fixed the problem.
http://gpsgate.com/products/gpsgate_client
Not sure exactly what it does, but once I installed it,OpenCPN say several COM ports that were not there before, and viola ! I had my GPS connection.
I am not using a puck style GPS. I borrowed a hand-held Garmin GPS that has a USB interface, just to test things out. My boat has GPS, so I am hoping to eventually pull the GPS signal from the SeaTalk network and use my laptop as the chart plotter.
I put some of the links I used (for the OpenCPN program, NOAA charts) on my website :
http://www.wcwebs.net/johnson/Hunter280/links.htm