Hi Sam,
I have a DNS-323 and two DNS-343's setup with ffp installed (see
http://wiki.dns323.info/howto:ffp) so that I can run Avahi and AFP. By connecting to the DNS's using AFP (not SMB), I am able to manage a 115 MB iPhoto Library* over a 1 GBit Ethernet Switch. I did try a 100 MBit ethernet switch, but it is a bit too slow to manage an iPhoto library.
Give this a try and let me know if you have any follow up questions.
Cheers!
* My largest iPhoto library is 115 MB. I actually have many iPhoto libraries that I manage in order to keep the size of each individual libraries down. All-in-all, I have around 400 MB total in my multiple iPhoto libraries. If you don't have it already, I would suggest investing in the iPhoto Library Manager (
http://www.fatcatsoftware.com/iplm/) -- this is a 3rd party application. This really handy tool allows one to quickly switch between libraries as well as build new libraries. In fact, if your current library just won't copy over to the DNS, you may want to consider splitting it into multiple libraries using the iPhoto Library Manager.