Is there a negative impact to using SQL Server with a lower compatibility level

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http://serverfault.com – We have SQL Server 2008 R2 which we are using for a database with a compatibility level set as 2005 (90). We will by upgrading it to 2008 at some point, but in the meantime I would like to know if having the database in a lower compatibility level is this going to have a negative effect on its performance? I found this question that implies there could be a negative effect, but it's for an older version of SQL Server. (HowTos)