I am about to launch a beta site, and heroku looks like a great option. The only think that is getting me down is that the only search option is $20/mth for the Websolr
This post seems to have good options:
Leveraging the full text search of postgrSQL:
http://tenderlovemaking.com/2009/10/17/full-text-search-on-heroku.html
Also explains the options of Ferret and Solr.