Merge Replication Snapshot Files
There is a lot of information here,

http://msdn.microsoft.com/en-us/library/ms151769(v=sql.105).aspx


And here,

http://msdn.microsoft.com/en-us/library/ms152502(v=sql.105).aspx


So the thing to be aware of, because I was using parameterised filters the snapshot folder above doesn't contain any data, only schema.

Also I was not filtering correct using SUSER_SNAME() so the filtering was not using the snapshot at all causing me performance issues.

Once that was sorted I could see in the snapshot folder there subfolders with a snapshot for each user of the system. This data is the data filtered for that particular user.