Rails - Apr 2006 - Page cache and query string

I''ve read about the problems of using page cache when there''s
a query
string, i.e. /article/list?page=1 will cache /article/list.html, then
/article/list?page=5 will retrieve /article/list.html regardless of
query string.

I''m using a workaround, it looks almost obvious but since I
haven''t
found it mentioned anywhere I''m afraid there''s some equally
obvious
drawback that I''m missing.  If that''s the case, could anyone
familiar
with caching in Rails please point it out?

Basically I''m having the web server rewrite URLs of the form
http://www.site.com/foo/bar?a=b to
http://www.site.com/foo/bar/query/a=b.  Then in config/routes.rb there
is:

  map.connect(''foo/bar/query/:query_string'',
    :controller => ''foo'',
    :action => ''bar'')

In foo_controller.rb:

  class FooController < ApplicationController
    caches_page :bar
    before_filter :merge_query_string

    def bar
      render :text => "You asked for #{params.inspect}"
    end

    private

    def merge_query_string
      params[:query_string] or return

      params.
        update(CGIMethods.parse_query_parameters(params[:query_string])).
        delete(:query_string)
    end
  end

When a request comes for /foo/bar?a=b, it is cached as
/foo/bar/query/a=b, and when it comes for /foo/bar?a=x, it is cached
separately as /foo/bar/query/a=x.  Apparently it''s working. 
Where''s
the catch?

Thanks for any insight.
Massimiliano