Maximum number of files in a folder?

I am preparing to open a wordpress multisite that specific people will create sites. Each site have 10 database table. Using Mysql 5.5.16 as innoDB. If that wordpress setup will use 1 database, how many sites 1 database can handle? And will be any performance problems after 30k?

I found this:
http://stackoverflow.com/questions/466521/how-many-files-in-a-directory-is-too-many
but couldnt sure about it.

server is:
http://www.server4you.com/root-server/server-details.php?products=5
so hard-disks are 2GB but SATA II, 5,400 rpm

df -T

Filesystem Type 1K-blocks Used Available Use% Mounted on
/dev/md1 ext3 1890807696 4935636 1788275184 1% /
/dev/md0 ext2 505508 28304 451105 6% /boot
tmpfs tmpfs 16468196 0 16468196 0% /dev/shm