I bought the Tomtom XL a couple of weeks ago and found it overall to be a reasonable quality sat nav. Admittedly this is my first sat nav, but this is a functional and easily accesible sat nav.
The menu systems are fairly intuitive and easy to get the grip of. I've hardly had to use the manual to get going and work out how to do things which is obviously a plus. The maps themselves have mainly been fine, but here and there it has tried to send me through a deadend or down a one way street(!). This can be amended manually when you come across a mistake and then shared with other users online.
One of the major negative points of this Tomtom is the mount however. All you have to do is go over one rocky bit on the road or pot hole and it goes flying. Makes one a bit nervous as I almost served when it plummeted onto my steering wheel! Thus, I've had to invest a further £10 in a decent quality mount which I would say is essential so factor that into the price.
Overall a decent GPS for the car for the money if you can handle the couple of negative things I've outlined.