[Dovecot] Maximum Folder Size/Number of Messages

[Ropetin]

I hope I'm asking this question in the right place,  I don't want to offend.

I've recently put together a proof of concept Dovecot IMAP server, and 
I'm very happy with its performance up to this point.  I'm looking into 
using it to replace our existing POP3 server, allowing users to store 
email on the server rather than on their local machine, hopefully 
avoiding loss of data.  The big question I have is, is there a realistic 
maximum realistic folder size, either in reference to number of messages 
or total file size with Dovecot?

I'm using Maildir and running it on Debian Linux x86.  Right now the 
filesystem is Ext3, although once the system goes live I'd be looking at 
something a little more fault tolerant and able to handle the large 
amount of data.  Any recommendations you may have on Filesystem choice 
are appreciated too!

Thanks,
Ropetin.