It is possible to have topic-title in the link instead of the number, but you need to be running the very latest version of bbPress from SVN, which is likely to be buggier than the official releases. The Download page has both.
Once 1.0 comes out, it will be a standard part of the release. There was much discussion on how to include a ‘prettier permalinks’ structure into bbPress and this was agreed upon and is committed to the TRAC development version of bbPress. I personally love it!
It works if you are willing to download the latest TRAC version from http://trac.bbpress.org/browser/trunk/ and then scrolling down to the bottom of the page and clicking the ‘download in other format – Zip format’. That is the latest development version. Then you have to change your config.php to have:
$bb->mod_rewrite = 'slugs';
Your .htaccess file should just be back to whatever you had before. Mine is just the + MultiViews part.