We are seeing a lot of SharePoint environments not yet on SP2. In your maintenance plan you should put as soon as possible the installation of SP2 because you will run an un-supported environment after 24/April/2010.
Edited on 24/Mar/2010;
Cleaned up some misunderstanding and the date will be 13/Jul/2010. Result is that August 2010 CU needs definitely SP2 installed. See also the updated link on the lifecycle page.
Information about the lifecycle you can find here: Lifecycle information for WSS V3 SP1 and the same is valid for MOSS 2007.
Resources for SP2 you need to check before starting with the idea to install SP2:
On http://technet.microsoft.com/en-gb/office/sharepointserver/default.aspx you can find: Content by Life Cycle --- Apply… Apply latest update: Service Pack 2. Before you install SP2, read important information about SP2 in the SharePoint Team Blog.
Easier way is to look with the SP2 tag: http://blogs.msdn.com/sharepoint/archive/tags/SP2/default.aspx
Also the blog of our sustain engineering team: http://blogs.technet.com/office_sustained_engineering/archive/tags/Service+Pack+2/default.aspx
Please test as usual an upgrade in a test environment where you have also all customizations and “add-ons” installed so that you get a feeling how this might work on production. Your disaster recovery plan is Ready?
If not please check the result of this query first and develop your own plan before thinking about any upgrade: http://social.technet.microsoft.com/Search/en-GB?query=disaster%20recovery%20sharepoint&ac=1
Best of all is that you will have a healthy system, you know what to do when the environment might be down and when asking our support it will be faster to find a solution.