In my new update for the WSP Listener I need to save a file from a document library to disk. This can be done by the following code:

// item is an SPListItem
 SPFile myFile = item.File;
DestinationFile = Path.Combine(@"c:\temp", myFile.Name);
if (File.Exists(DestinationFile))
{
   // Remove the old file
    File.Delete(DestinationFile);
}

// Open the binary data
 byte[] data = myFile.OpenBinary();
using (FileStream stream = new FileStream(DestinationFile, FileMode.CreateNew))
{
   // Save the file
    BinaryWriter writer = new BinaryWriter(stream);
   writer.Write(data, 0, (int)myFile.Length);
   writer.Close();
   stream.Close();
}

Have fun!