text column constraint, newbie question

Hi,

I'm new to both PostgreSQL and web-based application development; I
read the FAQ at postgresql.org (perhaps this discussion group has
another FAQ that I haven't found yet?) and didn't see this addressed.

I'm creating a table with a column of type text, to be used in a php
web application, where I'll be accepting user input for that text
field. Are there characters, maybe non-printing characters, or perhaps
even whole phrases, that could cause problems in my database or
application if I were to allow users to enter them into that column?

If so, does anyone happen to have a regular expression handy that you
think is a good choice for text columns' CHECK constraint? Or maybe a
link to a discussion of this topic?

Thanks!