If you ever want to check if a document library item's author is the current user, here's the code snippet on how to do it:

SPFieldUserValue authorUserValue = new SPFieldUserValue(myWeb, myItem["Author"].ToString());
if (myWeb.CurrentUser.LoginName == authorUserValue.User.LoginName)
{

// your code will go here

}

Hope this takes away pain from anyone trying to use GetByID

P.S.: sorry all of you I haven't yet replied to your emails - I've been on the road and jumping airports a lot, so life is kinda hectic which is making it hard to keep up with my mailbox.