A more concise, but less fun, question would be, "What don't you use Perl for?" The lists would be much shorter. :)
- Blog platform (in Catalyst).
- Parsing data from diving websites and writing into Excel sheets.
- Server health checkups.
- Converting broken, nasty Project Gutenberg HTML to clean XHTML and automatically posting it.
- Ajax forms and user voting.
- Jokes, like Acme::LOLCAT.
- RSS/Atom writing and reading.
- Automatic tear down and rebuilding of databases; DBIx::Class::Schema::Loader + DBICx::Deploy.
- Reminder emails.
- Date counters and parsers.
- Graphing weblog stats.
- Filtering mixed text+html perfectly to clean XHTML with DWIM paragraphs and newlines.
- Perl code coloring.
- Chat server.
- Typographical auto-markup; e.g., (r) --> ®.
- RTF --> HTML.
- CSS collapsing and style inlining.
- Perl controlled rsync as part of build scripts.
- Colored XHTML document revision diffs.
- Tax calculators.
- Order tracking and manipulation.
- Language translation services.
- Search engines; raw, metaphone, vector.
- DB --> YAML --> DB.
- MP3 manipulation.
- Image stamping.
- Et cetera, et cetera