It is known that ext2/ext3 FS have a rather low limit of about 32k files/directories per directory.
It looks like ReiserFS is limited in practice by the r5 hash function which allows about 1 200 000 file names without collisions.
But what about other common Linux File Systems? JFS, XFS, Btrfs, Reiser4, ext4,...
Thanks in advance!
EXT4 either has the limit of 64k or no limit, depending on which wiki you read (I assume that earlier versions had 64k limit and newer have no hard limit). It is still limited by the maximum count of links the Directory Index can contain, and that depends on that particular filesystem attributes (block size for example).
XFS, AFAIK, has no limit, so does Reiser4. Out of my head I wouldn't recall the case of other filesystems; VxFS is definitely very robust and if it has a limit, it's very high (not sure how much helpful this information is :-) ).
visit wiki link
http://en.wikipedia.org/wiki/Ext4
http://en.wikipedia.org/wiki/Ext3