I think it is getting a better read on GPS satellites. I'm putting mine in the car once a week or so, but I'm sort of playing with it in the house, and it's on 4 of 5 bars.
I had posted a question to TT techs 2-3 weeks ago, and they finally got back, with an apology, this week. I wanted to know about using the TT910 to do route planning from my computer, but forgot to tell them I used a Mac. While I waited for their response, I found that the feature -- using an image of the TT910 screen on your computer to control the GPS -- doesn't work on a Mac.
I also asked what improvements were in 6.51. The response:
"The 6.51 update includes:
Support for the TomTom RDS-TMC Traffic Receiver for Europe.
Safety Cameras - it's now easier to manage your Safety Cameras. Safety Cameras have been removed from the list of POIs. To enable or disable Safety Camera warnings, tap these buttons from the Main Menu: TomTom PLUS services > Safety Cameras > Enable/Disable warnings. The list of POIs is also easier to use, as it no longer has lots of entries for Safety Cameras."
I've responded to ask if the improvements will affect the TMC for US TomToms when they arrive.