I have had my 660 for about two years now and have never ventured into the POI world until I ran into this site.
I registered, paid my fine (kidding) and logged in then off I went to download land.
These are great, I am just now trying them out.
My problem is... I downloaded a bunch of POI's to my home computer, loaded them into my Garmin and hit the road for work. ( I travel a lot)
The POI's were great. I even received a proximity alert for a gas station but I was almost in the parking lot when it went off.
Sooo I thought I would try to edit the distance. I thought that I needed to do that with the drop down box when I downloaded the GPX file.
I tried to add a couple of new files to my Garmin (thinking I changed the proximity in that drop down window) but when I viewed them after adding the two newly edited files on my GPS, I found all of my original POI's I had loaded from home before I left were gone and only the two test files were loaded........NUTS!
So off I went on my company laptop to re download them again from the site.
By the way, I did learn in the forum about how to properly change the distance on the alerts. I did it in the POI loader and selected Manual instead of express.
Each time you use POI Loader, it loads only the things you have in the directory you have chosen to send to the GPS. It overwrites the original POI.gpi file in the GPS, hence the files you are missing after last update.
If you have a look at the directory in the sat nav "whilst connected to your computer" you will see only one POI.gpi file and it stores all relevant info in that file and sorts it out through it's own software program in the GPS to display on screen.
I encountered a very similar issue and found out how to do it through the POI Loader after a bit of playing around.
You'll always have the odd annoying POI going off at you. I live across from a school and it annoyed the hell out of me every time you go to something. For those odd ones you might be best of deleting the line.