Been using Maptech's Offshore Navigator for five years now. I have it installed on two laptops, as well as my home desktop computer. Being an old salt, fixed in his ways, as well as a navigation nut (taught piloting and celestial navigation), I insist on electronic reproductions of paper charts. That means raster charts -- which, in effect, are "photos" of real paper charts. They look exactly the same, and I carry both.
Electronic charting is very useful for voyage planning, as well as enroute monitoring. I connect one of my twin Furuno GP31 units to the laptop (it also goes to the VHF/DSC), and it displays the position of the boat right on the raster image. In practice, I've found it usually to be be extremely accurate.
Thus far I have eschewed all forms of dedicated chartplotters because they all use vector charts. These don't look anything like real paper charts (my main objection) and, due to the manner in which some of them were digitized, they may include errors of commission and omission. Chartplotters have the advantage of lower power consumption, waterproof construction and dedicated operating systems which are more robust than, e.g., Windows. But, so far, they only take vector charts.
Recently I stumbled upon a pocket PC solution which handles raster charts. Not new technology at all, but a very neat and very low cost package. My IPAQ 3850 runs a Maptech program which displays raster charts, and it takes a 20-channel GPS plug-in card, so you can see the boats position just as you can with the laptop-based setup. This used pocket PC, with all connecting cords, ALL U.S. raster charts on DVD, Maptech software, ActiveSync and Memory Map, plus a 1GB expansion card in addition to the 64mb internal memory, and misc. loaded programs (Excel, Word, Internet Explorer, etc.) cost just over $200. Great little device to have in your pocket in the cockpit, or in the local bar or wherever you do your planning/dreaming :-)
There are lots of other electronic charting solutions, but these two work for me.