I have successfully used POI Loader (on a Mac) to upload the gps team UK Speed cameras to my c510. I now have a poi.gpi which should contain the camera info and proximity info.
However, when driving I do not get an alert when I pass cameras that used to trigger one.
If I go to the spanner icon>Proximity Points>and press Change... next to Proximity Alerts I see a tick in a box next to Custom POIs
The only thing I could see that might have been wrong was that Attention Tone was off in Navigation but I was not getting a visual alert either.
I have now gone and paid for a one off download from Garmin and can see that on my Sat Nav the following files have appeared/changed date;