The other day I came across an issue with a user.  My user was uploading a number of documents by the click and drag method that I have discussed in a previous blog about mapping a shared document location.  He had all the permissions set up correctly for other MOSS user to view his documents.  However, he was the only one that could see the documents he uploaded.  He was using the out-of-the-box Document Center that comes included with the Collaboration Portal site template.

As with any concern with a document library, it is always good to start with the Document Library Settings. 

Go into your Document Library in question.  Click on the Settings drop down and select Document Library Settings.

On the next page, select Versioning settings from the General Settings column.

On the Versioning settings page, you will see options for setting up content approval as well as version settings.  For this blog, we will pay attention to the last setting known as Require Check Out.  To turn off all the documents being automatically checked out to the user uploading, select No for Require Check Out.

Now all the documents my user uploaded are visible to everyone he has set a viewing permission for. 
Required Check Out can be useful to assist in keeping changes limited to one user at a time.  However, for my user it became a pain because he was uploading 20+ documents at a time and then he had to check them in individually.  Experiment with it to see what works best for your SharePoint environment.