Here's what it comes down to for me. Price. Right now at Sam's Club you can get the TT Go 720 for 349. Nuvi 650 is a little over 100 dollar more. On top of that, it's got a 100% Satisfaction garentee through Sam's. I've got the 720, and for all it's cons, and as much as I try I can't seem to move to Garmin. I've spent a couple of hours in front of the Garmin 750, (not not the 650 but the upgrade to the 650), playing with it's features, looking at route demos, ect.
It cames down to several things for me. First, as much as I try to I can't get over the display on the Garmins. The maps look like a 5 year old took some magic markers and drew the maps. On top of that if you look at the nuvi forums, a lot of people complain about the redraw rates on the 600 series. I've heard that's been fixed in the 700 series nuvis but from what I saw at Sam's Club, it's still pretty slow. Also many have said that the internal antenna in the 700 series had problems keeping a GPS fix. There's a huge thread on the 700 series at pocketgpsworld.
Second, lack of features. Dollar for dollar, the 720 has more features than the 650. Plain and simple.
Believe me, I tried really hard to find a reason to take back my Go 720 and use a Garmin. They have many more POIs. Some of that can be fixed with custom POIs, and it might just be the fact that I live in Alabama, and well....how many "real" POIs are there in Alabama

, but I always walked out with my 720 in hand.
As for your cons:
-Various bugs (like shutdowns, etc)
I haven't seen any since the last software upgrade
-TT Customer Service (including internet)
I've had really good luck with them...just be patient and knowledgeable.
-POI are not sorted (can't pick "Italian" under food)
Nothing you can do about that.
-Cannot call the place directly from the Unit (apparently)
That's not true. I've used it. Matter of fact I've created my own POI files and formatted them to do this very thing.
Hope this helps.