[OOPS, I misunderstood: I thought y'all were looking for input on Basecamp functionality, regardless of platform, and just chose the Mac heading cuz you had to choose one. My bad.]
First, some background:
I'm a Garmin newb with a Vista HCx. I mostly use it for mapping personally owned acreage on foot. But I also play with geocaching and sometimes use it in the Car.
I think I'm almost an expert at Google Earth & I am a systems engineer, so not a technophobe. Also, I've not read this entire thread, so apologies.
In general, I would like to use Basecamp (or Mapsource) to:
1. manage the data on my eTrex
2. calculate (and recalculate) routes for experimentation before the journey
3. record waypoints I've discovered and share them with others (who don't have Garmin's or GPS at all, maybe via close integration with Google Earth .kml/.kmz, Google Maps etc.).
Compare & Contrast w/ Mapsource:
* Basecamp seems to allow me to save routing methods with each route while mapsource does not. Good! I might have a foot route (point to point) and a car route.
* Basecamp doesnt have waypoint categories (BAD). I seem to use that a lot so that I can quickly pick out waypoints I download from my eTrex from the "semi-duplicates" I already have in mapsource.
* Basecamp will let me playback tracks with elevation (GOOD) but mapsource wont.
So, back to generalities, specifically item #1 above:
I bought the eTrex for its small size. The ideal GPS for me would be the size of a coin, but that's totally impractical: You need SOME real estate for a screen and input buttons. The smaller the device's size, the more dependence I have on connecting it to a PC to interact with it.... at "base camp". ;) The PC software should be able to (among other things):
* add/delete/modify waypoints, routes, etc directly on the device
* add/delete COLLECTIONS of these things on the device for a given task at hand (i.e. one collection for a road trip to my parents, another collection for hunting at the lease, and another collection for "day-to-day stuff around town like geocaching & bicycling in the neighborhood"). This is because having 15-jillion waypoints in the device all the time makes finding the one you are interested at any given moment more difficult.
* add/modify/categorize/delete POI's - be they collected from sites like POIFactory or supplied by the maps, or your own .csv files.
* manage the waypoint symbols that the device can support, or at least limit myself in the PC software to those symbols that the device has onboard.
* limit my input fields to those supported by the device (e.g. 14 chars for waypoints or routes on the eTrex).
Maybe, if I get a second or 3rd device for the car(s) (Nuvi or whatever), having software that can store collections of data for each device would be helpful. Maybe I'd put road trips on the Nuvi, then bike/foot trips on the eTrex, and a combination of these on the device in my Pickup Truck.
Hope you find this helpful,