Good place to regenerate tags file and reload it for a given project

[jch]

Hello,

I'm very happy to have found:

http://groups.google.com/group/gnu.emacs.help/browse_thread/thread/20d91bdd662cb7ea/3de64d350b9b31c0?lnk=gst&q=auto++tags+#3de64d350b9b31c0

which lets auto reloads a tag file after it has been regenerated.  I'm
2 questions away from a very amazing Etags experience.

1.  What's a good way to regenerate a tags file when the files that it
indexes have changed?  Currently, I naively reindex every 20 minutes
in a cron job.  Ideally, I would like incremental reindexes to update
the tags file with recent changes to files.  I'm not sure if etags is
capable of this, or if there's a combination of Unix tools that are.

2.  What's a good way to automatically load a tags file for a
project?  The way I've thought about doing is to look for a tags file
in the current directly, and then recursively look for a tags file in
my parent directory.  Does anyone adopt this approach, or something
similar?

Thanks in advance,
Jerry