I found this on the official forums. It tells you how long until your account goes inactive (from not logging on I think) and how long until they delete it. Note that if you plan to be away for a while use the vacation mode under 'options'.
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Feature - Inactivity deletion will immediately be performed in regular intervals

* Phase 0: If somebody takes no action within 5 hours after registering an account, it will be immediately deleted.
* Phase I: Within the first 7 days: - Time until inactive: 2 days - Time inactive until deletion: 2 days
* Phase II: Two weeks up to a month: - Time until inactive: 7 days - Time inactive until deletion: 4 days
* Phase III: 1 month to 3 months - Time until inactive: 7 days - Time inactive until deletion: 14 days
* Phase IV: from 3 months onward: - Time until inactive: 7 days - Time inactive until deletion: 30 days