Backup?

Hello,

I had a look for 'backup' on the mailing list archives and strangely
enough didn't find a message containing the word in admin, general
and sql mailing lists... I am sure this must have been asked before,
but still:

Would it be possible to backup a db by just copying the dir struct
under the PG_DATA or must I absolutely use pg_dump? I am
using Postgres 7.0. The purpose of the backup is of course to have
a copy handy if eg the harddrive breaks. As I understand pg_dump
could be comparatively slower, plus it produces a text format
dumpfile, which could be kind of large in my db in future.

Thanks in advance,

Emils