Well, the new quests have again proved that they can contribute to the lag, as you will see tomorrow morning.
We all know what a nightmare Flash is anyway, and various other elements also contribute (loads of buffs for instance).
database corruption too, especially when an exploit like the Parrot one is hugely abused, it actually took down 1 server and forced a roll-back.
Funnily enough, problems on my german server over a year ago caused the chat-server to malfunction and even the mail was flaky, yet the gameplay was remarkably good, which makes me wonder if they too contribute.
But, the number one factor is still the servers themselves.
One of the reasons I loved playing the French server so much was the speed. lag was almost non-existent, and it even outperformed the much better specced German servers, which in turn were faster than ours here. Considering their geographical locations and my distance from them, this was a real eye-opener, my closest ones were the slowest, the mid-range was the fastest and the furthest wasn't too shabby either.
Then came a major change, whilst the german performance remained about the same, the other two collapsed drastically and now the closer the server, the worse the performance.
This makes no sense, unless there have been hardware and/or location changes (including changes of telephonic network).
No wonder these 3 seem unable to shake the 'beta' tag.
Oh, and even 'background' tasks don't seem to tie in with game performance, whilst sometimes a Windoze update will appear to slow things down, another time downloading and installing an 8Gb game did not impact at all.
The only thing that clearly made a difference was having the test server open, not only did it kill Flash often, but it dragged down the Live games to its snail pace, whereas having French, German and UK servers open simultaneously does not.