I've set up both mediatomb and minidlna on my ubuntu 10.04 PC. They both stream media perfectly to my Android phone (Samsung Galaxy) and Google TV (Logitech Revue) using UPNP. Yet my laptop (Ubuntu 11.04), does not see my PC's services on the network.
Forgot to mention that, on my laptop, I've tried both boxee and totem, with the Coherence plugins, with no results.
What software are you using as a client? Or are you looking for a software recommendation?
If you are after a software recommendation, Ubuntu's default movie player (Totem) can act as a DLNA player if you install the totem-plugins-extra package. Once the package is installed, start the movie player and pick Plugins... from the Edit menu. Check the checkbox next to Coherence DLNA/UPnP Client and you should be good to go.
Open the movie player's side bar and select Coherence in the drop down menu. You should now be able to browse the DLNA servers on the local network and start playing movies or songs by double clicking on them.
UPnP plugin no longer available in Totem 3.0.1. Looks like package maintainer has removed: https://bugzilla.redhat.com/show_bug.cgi?id=694507
