the bluechart kit comes with an sd card.
the cd has every chart needed for the are covererd, and there big areas ie - all of europe or all of north america, you transfer the charts to the sd card then shove te card in the magellan. now, here's the good bit compared with garmin. Every chart is unlocked, unlike the garmin, where you buy an unlock code for every chart area you need to upload. the official line from magellan is you can only upload one chart at a time, loading a different chart overwrites the current one.... but its a standard SD card. so stick the card in a card reader and copy the chart image file and rename it. Each time you load a chart to a card from the bluenav software it always calls it 0001.IMG or something, so if its renamed on the card - it doesn't overwrite it! there's a menu option to switch charts on the unit itself when you shove the card in the unit. with a 1gig or 2 gig sd card, if you spend the time doing it you can get every chart loaded on the card AND keep a backup in a folder on the mac!
I did read a couple of threads on the web elsewhere that suggested you could convert the magellan .IMG format to use elsewhere, but never found out how
I paid £125 for the bluechart kit over here, which I think is a bargain as every chart in the kit is available to use, unlike bluechart
as for chart quality, I can only vouch for the UK charts as they are the only ones I've used, they are derived from the standard UKHO vector charts and every bit as good as the others IMHO - C-mpa, Garmin and navionics, slightly different styles, but just as detailed
they look something like: (this is the 2002 version)
http://ebgb.net/misc/tyne-entrance.png
I only know one george that is sailable, but only after he's had plenty of rum, and even then doesn't handle very well in a slight swell