Good article, but a couple of clarifications are in order:

First, FILESTREAM is a storage attribute on a varbinary(max) datatype column. It is not a new datatype. Seems like a trivial difference, but it has important implications. Primarily, client code doesn't have to know anything about FILESTREAM. to a TSQL client, it's just another varbinary(max) column. The ONLY difference a client would notice is that the blobs can exceed 2GB.

Second, there is a supported way to access the individual files UNDER SQL CONTROL. Using the column.GETPATH() function, you get a logical path (not in the physical filesystem) which you use to open the file by calling OpenSqlFilestream. This gets you an open file handle which is enlisted into the current SQL transaction. Any modifications are done as part of that transaction, triggers fire when you close the file, etc.

The physical files are ACLd to the SQL service account only, so unless you're running as that account, or you are a box admin walking on file security, you can't access the files outside of SQL control.