Here are my notes for upgrading to Service Pack 1 when using the multiple community setup described in this article:
Community Server - Setting Up Multiple Communities.

1. Run the update SQL script that comes with SP1.
2. Copy all the new files to the CS Web folder. I'm working with the source and it is in Subversion, so I exported the CommunityServerWeb20 (Internal) to the Web folder on the server. Then I manually copied all the bin files. If you are building from source, note these tips:
   1. use right version of config files - for ASP.NET 2.0, you have to copy the config files from the ASP.NET2_configs folder.
   2. set the build type to release in Visual Studio.
   3. add a reference to CommunityServerWeb20 (Internal) for lib/Framework2/CommunityServer.ASPNet20MemberRole.dll
3. Copy Web/blogs folder to each community. (See the original article for details.) I deleted all files in the target folders, but I made sure I did not delete the placeholder folders for user created blogs. Then I copied all the new files.
4. I don't believe files and photos folders had any files that changed, so I didn't make any changes to those folders.
5. According to my original article, each community has completely independent themes.
   1. I had customized the site skins for some communities, so I only copied the SP1 changed files to each community. These are the files I copied into the appropriate folder in each community:
      1. /Web/Themes/default/Skins/Skin-Editor-Enhanced.ascx
      2. /Web/Themes/default/Skins/Skin-Editor-Standard.ascx
   2. I had added some custom blog skins, but I had not customized any existing blog skins. Therefore, I copied the entire /Web/Themes/Blogs folder to each of my communities.
6. I did not detect any changes to any of the config files with the changes in SP1. Therefore, I did not alter my custom config files for each community. However, I did alter the trust setting as described in my earlier article.