It is limited only by the amount of free available memory on/in (SD card) with your nuvi. On my 760, I have installed a 4g SD card. On it, I have some 124k POI (4K of which are caches w/ 5 logs - the rest are locations of: Home Depot, Lowes, Dunkin Donuts, Bank of America ATMs, Quiznos, All the 144mhz, 440mhz, 29mhz and 50mhz ham radio repeaters in the entire USA, etc - you get the idea) Also on the card, I have the 2009 maps for the US, a couple dozen or so photos, and about 300 MP3 music files.
Does that help??
Steve
Yes thanks - so in principle you can store quite a few caches as POI assuming that you don't fill your nuvi with all sorts of other stuf!