Is there any interruption of service when switching recovery models? I need to switch to FULL recovery model for several SQL Server 2008 databases. However these are in production. Whilst doing these things out of hours is good practice I wanted to plan for any down time or interruption in service, no matter how brief.

Does anybody know the impact changing the recovery model to Full has on a production database?

Clarification: I have a whole process scripted (backup's and logging) and tested for log shipping and restoring the other end. However the one thing I couldn't find details on was if changing the model would have an impact on availability or performance during the process.
I've never had any issues from switching from simple to full. You will have to consider your backups tho.

Microsoft has some information about making the switch in the link below, 

http://technet.microsoft.com/en-us/library/ms178052(v=sql.105).aspx