I think it's a real shame that Google didn't buy either Telenav (acquired by Tom Tom) or Navteq (acquired by Nokia).
I'm guessing you mean Tele Atlas, not Telenav.
One example of a Tom Tom PITA is when driving from here (in Canada) to a location in the US. Even though the maps for both may be loaded, you can only navigate a route up to the border. You then have to make a new route once you're in the US. In other words you can't pick a destination unless you're currently within the same country.
This problem indeed existed with the very first versions of the maps they released with their TomTom GO range, and I agree it was a PITA. But they fixed that problem years ago and now you can use seamless maps without a problem. It works great.
I'll be the first to admit the TomTom software is badly designed though. Their HOME application sucks tremendously eg. And the problem Patrick experienced is too stupid for words. It has been reported to them for ages now yet it still continues to exist...
That's why my first advice to *any* new TomTom owner is always: before you do *anything*, make a complete backup of the thing by copy/pasting the entire contents of its internal flash/SD card to a safe location on your computer. Do this via Windows explorer as well, NOT via the backup option of the HOME software, because, as said before, it sucks. If something should go wrong, reviving your TomTom device is as easy as re-copying your 'backup' back to the device.