I propose to change the default value of allocationSize for sequence columns from current 10 to 1. It's defined in $definition['allocationSize'] in Doctrine/ORM/Mapping/ClassMetaFactory.php.
The improvement request is based on detailed discussion on http://www.doctrine-project.org/jira/browse/DDC-569?focusedCommentId=12855&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12855
Current default value for allocationSize=10 is CONFUSING and I am sure it will cause problems and misunderstoods for many people in future.
The core of the problem is that lot of people define table structure manually, separately from entity annotations. And while the default allocationSize is 10, they have to remember (and they have to know they should remember) each time they write new table and new entity, that:
a) They have to define each the sequence in database manually with INCREMENT BY 10
b) OR they have to define in each entity manually the annotation for @SequenceGenerator - allocationSize=1
c) OR they have to manually use strategy="IDENTITY", but it's primarily related to primary keys, not to all sequences at general.
Shortly, in an intuitive way everybody assumes the behaviour as allocationSize would be 1. Current default value 10 is not in accord with this intuitive perception and will cause many questions and misunderstoods.
The "preloading" of 10 values at once is a kind of "advanced optimalization" - it's great it is available and implemented - but it should not be applied automatically, but only after explicit setup.