Many times, I upload multiple documents to a library that requires Check Out. Once the files are uploaded, SharePoint keeps the documents checked out and there is no immediately apparent method to check in all the documents at once.
In WSS, you'll need to manually check in each document. Get your clicking finger ready!
In MOSS, there is a much easier method to do a mass check in, but it is not obvious. My approach uses the Content and Structure interface available in MOSS publishing sites.
** Note: Your document library doesn't have to be in a publishing site. It just needs to be a child of a publishing site.
Here's how I do it.
All done.
The Content and Structure interface is very powerful and you should use it to accomplish many bulk tasks within MOSS.