I just found out the hard way that upgrading to 8.2 (or I think even 8.1) can be a challenge if you are using UTF-8, as versions prior to 8.1 allowed invalid UTF-8 characters.
This will result in errors like:
invalid byte sequence for encoding "UTF8"
To solve this run your dumpfile through iconv:
iconv -c -f UTF-8 -t UTF-8 -o cleanfile.sql dumpfile.sql
as desribed at http://www.postgresql.org/docs/current/static/release-8-1.html (right before chapter 7.3).
Furthermore the import might fail because of a bug where tsearch2 is storing invalid UTF8 characters prio to postgresql 8.2 (http://www.dbtalk.net/mailing-database-pgsql-bugs/re-bugs-copy-fails-8-a-341028.html)