How many files in a folder is too many? Many years ago I vaguely recall that the Finder in Mac OS X would start having problems if a folder contained 2,000 - 3,000 items or more.

Apple doc says that the HFS Plus file system has a theoretical limit of a 2 billion files per folder all Mac OS X versions.

What is the practical limit?

Will having 10,000 photos in a folder be a problem?
You can easily try this yourself by running the following in Terminal

mkdir ~/t
cd ~/t
dd if=/dev/random of=test bs=1024 count=16
for i in {1..10000}; do cp test test.$i; done


to create a folder containing 10'000 files with 16kB each (replace the 16 in the third line with another number for differently sized files).