The default file upload size in SharePoint is 50 MB.  Sometimes, you may have users that need to upload documents that are larger.  This is quite easy to change.  Simply go to Central Administration -> Web Application General Settings.  Select the Web Application you want to change, and you will see a textbox to specify the maximum upload size.  Before I remembered to look here, I tried changing it the old ASP.NET way, by changing the following line in the web.config.

Interestingly, the file size specified here is also 50 MB, but changing it here does not allow you to upload a larger file into a document library.  I also figured I might have to change it to match whatever I had set in SharePoint but you don't.  You can leave it the same and upload a 100 MB file into SharePoint just fine (provided you changed the setting).  So from what I can tell SharePoint does not use this setting at all and it would only apply if you had written a custom upload form using ASP.NET.