I have a Nuvi 1440 which I am adding POI's to. Iy may sound obvious, but it is better to add POI's to a Micro SD card. THis can be done on the computer and choose computer rather that Garmin. When you insert it into the unit, it will say it has found them and do you want to copy to unit. Say no as this means all your POI's stay on the card and not on the unit. This is a benifit if you constantly update. It is much quicker to use the SD carn in a holder as the transfer speed is faster. Also there is no need to remove the old POI's sperately.
If you use POI Loader you only have to transfer one file as it combines all new updates into one file called POI.gpi and then loads it to the gps.
No editing of individual files required and much faster. It even gives you the oportunity to delete the redunant poi.gpi file which leaves more free area on the gps.
Everything will work faster from the GPS memory if you have the space to put it there.
Use the SD card for extra data that you do not access very often.