problems setting gitattribute ident for a whole directory

Hello. 

I'm moving from SVN to Git, started just two days ago. I'm amazed with Git so far, also using it with SVN solid.

I'm having few difficulties setting ident attribute:

1) Setting it for a whole directory. I tried .git/info/attributes,
.gitattributes in root of my project, I tried some patterns ( app/*, app/,
app* ), nothing work so far. Using app/* works for files placed in app
folder but I need to apply this attribute for a whole directory
(recursively). 

2) If applied correctly, will it work with files that already exists in
project ? 

3) What I need to do so that changes (replacing $Id$ with hash) will show in
all affected files ? I found some tutorial, where author applies this as rm
file; git checkout -- file. But how should I proceed for a whole project ?