I would like to know if there is a limit to the amount of POI you can put on the Nuvi 660. I have played around with it and I have found that if I have more than 26 files in the Custom menu, the POI loader tells me that there is out of memory. I have not got an SD card yet, but when I do get one will the POI loader install the POI's on the SD card and will the 660 read from the card or am I limited to the 26 files on the unit its self.
The POI loader will load into the SD card and the GPS will read from it, so you're limited to the size of your SD, (mine takes a 4gig) and I'll recomend that you transfer all (or most) of your POI files to the SD card, that way you free the memory (and therefore get better performance) in your Unit.
PS a 1 or 2 gig card is more than enough for this type of files
It will give you a choice, the SD and the unit have different drive letters (F or G) or something like that. F being the Unit, and G the SD card, that depends on how many drives you have in your computer.