Pings are dependent on the allies and foes you are connected to, since GW's PvP is multi national, you probably will get lag some times when connected to various players around the world.
If your into high end PvP, it's not that recommended due to our ISP, but still do-able, but I doubt your interest is in high end PvP though. For casual PvP, it's works quite fine, (generally 200-500).
For PvE, generally its around 200 to 400 in US, Korean servers from 100 to 200 in general(below 100 during good times), with occasional lag spikes due to our lovely ISP.
Do note with all the pings stated above, GW handles connections quite good since it uses instancing for the game. Even though the game mechanics is geared towards PvP, you can still stick to PvE if you want, not much problem there.
for me any ping not more than 400 is considered good already since we got a bloody ISP here.