Update--apparently Garmin has wised up and implemented at least two measures:
1) Starting with version 2.3, the app looks for the existence of "garmin" anywhere in the /etc/hosts file; to get around this, you simply remove all such entries and then install a third-party firewall app (e.g., Firewall IP) and tell it to block gold.garmin.com; once you do this, 2.3 will work...except...
2) 2.3 and up also does ALL server-side checks EXCLUSIVELY through gold.garmin.com so if you're blocking gold.garmin.com in your firewall program--this means no more being able to access the stuff in Extras (in-app purchases, including free ones)...and Google Local Search, Weather, Fuel Prices, traffic hacks will no longer work either.
So what does all this mean for jailbreak iPhone users? Either you stick with 2.2 or else purchase a legit 2.4. Like I said earlier, I don't care or need any of the "new" stuff that's in 2.3 and 2.4--I'd rather have a near-completely functional 2.2 than a crippled 2.3.