And the one other thing I have against X across the network is that it is "fat", i.e. uses up a lot of bandwidth, however freeNX, VNC etc can use compression across the wire to allow for less bandwidth usage.
I am not knocking using X over a network (although my previous posts my indicate otherwise) and indeed there are times when it is desirable. LTSP use X over the network, but TBH I have found that you are best using something like VNC or NX to allow rdp-like access as that is what they are designed to do and need very little on the client. Configuring X for the client can be a PITA, even using xming as dependencies need to be met and you are basically making each and every client on the network a server, thus opening more security holes....