For the 2d "classic client" I believe some of this is tied to the huge new memory leak. Friday after playing in the classic client for about an hour on one character, I logged out to switch characters. Trying to log in on the 2nd character it would not recognize my password. I completely closed the client, which freed all the memory up, and restarted and logged in just fine. One time thing? Nope. After playing on the 2nd character about 45 minutes crafting things in my home, I went to switch again. Same problem. Restarted the client logged right in. Yesterday, Saturday, I didn't play one character longer than 30 minutes and the issue didn't resurface.
Edit:
And another thing. Why does the 2d client utilize 100% of the cpu before you even login the game?!?!?!? 1.4Ghz cpu with 1GB ram and tons of drive space. Just launching client.exe and not even logging in the thing will sit there and chew up every available cpu cycle. This in turn heats up the cpu which then calls for the fan to kick in high gear. This is killing our PCs a little at a time for no good reason!