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http://classic.battle.net/diablo2exp/Quote (The Arreat Summit)
Ladder Reset October 25 - Nebu
We anticipate all Diablo II realms to be down for approximately six hours during the reset. More specific information on realm availability on the day of the reset will be posted in the Battle.net Status forum. When the ladder is reset all existing ladder characters will be converted to non-ladder. All characters and items being converted to non-ladder will remain intact, but once converted these characters will no longer have access to ladder content such as creating ladder-only rune words. For more information on ladder characters please visit the Arreat Summit Realm Character Types page.
Quote (The Arreat Summit)
Diablo II Ladder Reset March 28 - Blizzard
While our original poll for reset length showed a little less than 150 people wanted a reset every year, our most recent follow up poll had over 1,000 votes for 6 months: http://forums.battle.net/thread.html?topicId=27800569877&sid=3000
Quote (The Arreat Summit)
We generally prefer to provide a two week warning for the case of resets