I use it on a daily basis, fantastic bit of software. Expensive, but quick to load, find route and reroute if you miss turnings. I'd certainly recommend it.
I've got in on a 3G and love it.
The menus are a bit laggy but when it's in 'nav mode' it's fine.
I also got the TomTom cradle and that's great too.
Yes it's expensive, but to be honest it works out about the same price as a normal TomTom (£60 cradle, £60 app).
I'd rather have the app on my phone and use a cradle that also acts as a handsfree than get a separate device.
I haven't used the free/cheaper apps but I've never felt the need.
If you are used to TomTom and aren't put off the price then go for it.