I bought the TomTom 720 two weeks ago. I chose this model because it has auto re-routing, integration to my car stereo via its internal FM transmitter, integrated with my phone through blue-tooth, had a big screen, good reputation and would play MP3s (also through the car stereo).
It arrived in good time (thanks Play!), and I eagerly followed the instructions for installation to the letter. This was my mistake. If you go for any TomTom, after plugging the device into your computer, but before installing the latest maps and application software make a back up of EVERYTHING already on the TomTom (open its folder in Windows Explorer (shows as drive E or F) and copy all the files/directories etc into a backup folder on your PC). You'll thank me for that nugget of information! Then you can allow it to install all of its software and updates. I did the update without the backup and the downloaded application and map were corrupt - the corrupt application caused the box to flash a red cross. I sorted that with help from the internet (TomTom were rubbish!), but the map was another problem entirely. Once you've downloaded a map update from TomTom, you cannot download it again. If you had a problem with either application or map download you can use your backup to 'fix it' and try again.
I'm still waiting for the replacement box (TomTom's suggestion when their support ran out of ideas, and wouldn't allow me to download the map again), and hopefully Play will be as excellent as they were with the original delivery. I did manage to get slight use out of the broken box, and I can recommend it strongly (but BACKUP!), when it worked, it was smooth and did everything I expected even better than I expected. When used to generate and guide me through a route, it kept rebooting (which was frustrating), something I couldn't solve with all the help the internet had to offer.
The FM transmitter coupled with the BlueTooth connection to the phone allowed me to use the box as an in-car jukebox, with speed camera alerts and hands-free kit for the phone - all of which was flawless, and easy to set-up and operate. Using the box like that was a joy. It was just a shame I couldn't use it as a route planner!
In summary - if you're after a sat-nav and your budget will stretch to the 720, go for it! It's brilliant. Just remember to back it up before you connect to TomTom and you'll have the best sat nav on the market.