Hmm, yes, I remember following that conversation. Have you had any more luck with open source software since then? I'm reluctant to purchase software since most of the mapping I do at home on the mac is the volunteer sort. Although, that geocoding option in manifold looks pretty nifty and would be quite handy... but I'd have to buy the MapPoint extension. I think I'd be more keen to try to some open source GIS on the map if I knew I'd be able to export to illy.
For the US, you'd be able to get by with the Manifold geocoding database. I never checked how that performs, but I have to tell you I wasn't terribly impressed with using MapPoint Europe as a geocoding engine. Maybe it was my input data, who knows?
There's a number of free geocoding services available. Well, 'free' with some restrictions, but unless you want to do huge amounts of addresses per day, you'll get by.
As for open source software, sometimes it's great, sometimes it's not. GRASS is something I haven't been able to get to work, not on MacOS, not on Ubuntu. Not really sure why, but I don't have the time to tinker with it (and I have plenty of other tools with which I can do my work, albeit through VMWare if I want to do so on a Mac).
Still, I would recommend Manifold and Global Mapper. Excellent products and very affordable.