Having Devel module active on my site showing the list of queries executed, I can see tons of small fast queries made by path module looking for an alias for an specific url.

Fisrt I can see a bunch of duplicated entries on the list every single one of them executing 10 times loading the alias for the current node url. This is done by path_nodeapi function.
9.08 10 path_nodeapi SELECT dst FROM url_alias WHERE src = 'node/1'
8.93 10 path_nodeapi SELECT dst FROM url_alias WHERE src = 'node/1'

Second, and I think more important, I see a bunch of entries looking for aliases to comment edit, delete and reply links. This, on a page with a couple of hundreds of comments, gets very slow, even if every query takes a few miliseconds.
7.8 1 drupal_lookup_path SELECT dst FROM url_alias WHERE src = 'comment/edit/479'
7.32 1 drupal_lookup_path SELECT dst FROM url_alias WHERE src = 'comment/reply/1/479'
7.23 1 drupal_lookup_path SELECT dst FROM url_alias WHERE src = 'comment/delete/479'

Well, I don't really undertand what is going on on #1, why is executing that query 10 times, multiple times.

About problem #2, I think it would be cool if an Admin could set up a list of paths to avoid for path module. Some kind of list like blocks visibility have:
comment
comment/*

Then, if that is part of the url the module is looking for, it will dismiss it saving some valuable query time.

That list of course should be loaded once by the module when the page is starting to be generated.