Occasionally my PS3 refuses to find the media server and both have to be restarted. Not a huge deal, but annoying- especially to someone who doesn't know how to reboot the media server.
I have seen the same problem, but in my case I think I know the reason:
1. The DHCP server in my router hands out a new ip address to the PS3 every time the PS3 is booted.
2. PS3 Media Server keeps track of which PS3s (or other DLNA clients) it has seen on the network. This list is based on ip addresses, not MAC addresses.
The combination of these two behaviours is that the PS3 Media Server's list of known PS3s just keeps growing and growing over time, even though I only have one PS3. I think that the problem when the list is finally too long.
So the easy solution would be to use a fixed ip address on the PS3. I just haven't bothered yet.
I do agree to your reservations against using the PS3 as a media player. I think it is a great combined gaming console, internet browser, network music player, network movie player and blu-ray movie player. But everything except the gaming can be better handled by dedicated devices. I have already ditched it as a music player and have bought a Squeezebox Touch (which is almost as expensive as the PS3).