I'm not sure If this has been brought up, but player vs player had some inherent balance issues. Now D&D is about co-op and I'm under no illusions that designing it to be PVP is not going to take high importance. I still feel that it should be discussed as it can be a very fun aspect of multiplayer.
One of the issues that gave huge problems was Hide in plain site, as it left anyone with a good pool of skill points and access to non cross class skills to abuse Hide and move silently. Leaving players the absolute need to have true site. This nerfed the rouges tactics making them a useless option. As variety and choice is king this was a bad option. I did see some very heavy lag inducing heartbeat scripts that tried to prevent or slow down repetitive HIPS attacks that crippled Multiplayer servers.
Our own solution was to remove all "True sight" from items, and to only give "see invisible" on casting the "true sight" spell unless the player in question had heavily invested in both Spot and listen skills. This had a side effect of making Druids with dragon form very valuable when combating rogues.
A much preferred solution would have been to limit the frequency a rouge could hide. As a rogue equipped with a bow and HIPS was near impossible to target and attack in the same time that they could spam the sneak button.
There are a lot of things players can focus on to get past the rock paper scissors style game that D&D is in PVP, and attempt to make a rule everything top trumps character. Though the only two that really caused issues was Knockdown, and HIPS. As they were too inaccessible to deal with.
Thoughts appreciated peeps ?