Hi JontomXire
A few years ago, PvP elements have been quite popular in PS, be it pure OoC sparring, rp-fights, a mixture of both, or even large arena tournaments. Much of the interest in PvP was lost during some game rules balance issues when crafted armor and some defensive buffs were first introduced. Thanks to people like Eonwind, these imbalances have been widely resolved, and even many more improvements to combat mechanics are to be expected (either soon or soon
TM). However, I have the impression that players are still a bit hesitant to engage in PvP activity, even though it is well enough balanced for some fighting fun. Another reason may be that people like me are too lazy to host more combat-based events
Concerning PK, I think the game philosophy is to protect players and prevent grieving. So, everyone is free to accept challenges from other players (or turn auto-accept on via options), but otherwise PvP is restricted to certain zones, guildwars and group challenges. One thing that might be misleading here is that individual challenges are nonlethal (automatic yielding), while attacks during guild or group wars are lethal.
Theft is again another topic, and best explained by some rules dev or gm. As far as i understood, the corresponding skills (or at least lockpicking) have been implemented and released, but they are not functional (trainable) due to ... well, why actually? But I think the game philosophy will be the same, harming other players will only be possible with certain restrictions (like in dangerous places where new players are not expected to show up).