The out of box setting is 50mb. This is for a single upload operation. That means – a single user performing an upload operation to SharePoint. The upload cannot exceed 50mb for that operation. This could be a single file of 50mb or 10 files of 5mb each. Again, this is per upload operation. Each user performing an upload is a seperate operation. The other part of this is the 2gb limit. This is for a single file. The largest single file that can be stored in SharePoint is 2bg, due to SQL Server limitations (at least in SQL 2005). A blob in SQL cannot be larger that 2gb. Each file is stored as a blob in the SQL Server content database for the site collection. This is changed, somewhat, with SQL 2008 and its ability to handle remote blob storage, thereby letting you handle files larger than 2gb.
So the maximum size of a single file upload is 50MB when using the default settings and the maximum size of a set of files is also 50MB when using the default settings.
These default settings can be amended. The hard limit is 2GB.
See http://wss.asaris.de/sites/walsh/Lists/WSSv3%20FAQ/DispForm.aspx?ID=731 for where to change the setting.