Hello soundX
I'm not still jumped on the PSGI charriot, i've only done some little test, but i'm collecting links about the matter on my homenode for a future learning time.

YourMother++ for the example: your comments are always worth to read and to bookmark.

About the deploy of Plack apps you can read:
Re: Change cgi script to PSGI app
Plack and multiple domains
http://www.omakase.org/perl/starmanreverseproxyab.html (only Perl part is not in japanese)
http://suryahunter.com/wiki/hunter/perl_ironman/mount_multiple_apps_with_plack

HtH
L*