Web App like Google

[gene tani]

Yes, there's a lot of issues, cross-site scripting, session hijacking,
proper authentication, etc.   Open Web App Security Project is useful

www.owasp.org

Also, before you start with NLP and full-on parsers, think about if you
can apply a text indexer, stemming and stopping both your user's
queries and the database content.  Much easier conceptually, easier on
db server too.  and there's lots of good python packages/python
bindings.

http://www.xapian.org/
http://www.pypackage.org/packages/python-pyndex
http://www.divmod.org/Home/Projects/Lupy/