As of today’s patch (Thurs, 27 June), I started experiencing horrible lag. After logging in (if I even could) I could move around somewhat freely, but would occasionally freeze in place and find myself unable to move. If I tried to interact with any object or use an attack, I would “lag” out; chat still worked fine, but my abilities would simply flash without activating and I would be unable to move until an error came up and I was disconnected.
After several hours of this, including scanning the forums for some information, I tried something that worked for me.
Step 1) Download the GW2 launcher from the account management page
Step 2) Begin installing GW2 to a different location than your current install path
Step 3) Close the launcher and cancel the game download, and copy or cut/paste the GW2.dat file from your previous installation into the new install path, replacing the partially downloaded one. Run GW2 from this location.
I don’t know why this worked, or what the implications are as to the source of the lag. However, it’s a simple, fast, and harmless way that may or may not help (but fixed the game-breaking lag that I was experiencing 100%). I figured if this helps anyone, I might as well share.