Bring up pandora (not just the widget) and push menu softkey-there will be an option "quit".
I just bought a Droid 2 and was relieved to see this discussion thread.
Going to the Menu softkey while Pandora is playing did bring up a menu that offered the option to "quit" / a Full Stop and exit from the app.
To Pause and then hit the Home softkey option (also mentioned in this forum and what I tried first ) did not work for me because everytime I went back to Pandora, the song I ended on was still there, paused & waiting for me to resume.
Thanks Troops2990. I am going through a bit of a learning curve with the multi-use Droid 2 phone and appreciated your post.