leorussi's post helped me get started, but a specific file deeply buried in the Tunnelblick Content folder resisted. Hopefully, this will help others with the same issue.
Here's a short version of what (finally!) worked for me.
1. launch the terminal
2. cd ~/.Trash
3. tried sudo rm -rf Tunnelblick.app but got a long list of errors
4. troubleshooting
I noticed that the first error was different than all the rest:
Error 1: "rm: Tunnelblick.app/Contents/Frameworks/Sparkle.framework/Versions/A/Resources/fr_CA.lproj: No such file or directory"
Error 2 and all subsequent errors looked like this: "rm: Tunnelblick.app/Contents/Frameworks/Sparkle.framework/Versions/A/Resources: Directory not empty"
Basically, there's a problem with the fr_CA.lproj file. Obviously, the file exists, but it thinks that "No such file or directory". It turns out it's symlink to a file that doesn't (and never did) exist on my system. So the following steps get rid of that file/symlink. The subsequent errors are failed attempts to remove the folder tree that contains fr_CA.lproj and go away once that symlink is removed.
5. cd Tunnelblick.app/Contents/Frameworks/Sparkle.framework/Versions/A/Resources
6. tried ls to see if the file is present, which it is, so not helpful
7. ls -leO (note: that's "little L, little E, big O")
(This step largely thanks to https://sites.google.com/site/drazeidler/%22rm%22command-%22operationnotpermitte d%22.)
Shows much more detail, including permissions and symlink info.
These are the results:
total 8
lrwxrwxrwx@ 1 root wheel uappnd 84 Mar 15 03:44 fr_CA.lproj -> /Users/andym/Development/Build Products/Release/Sparkle.framework/Resources/fr.lproj
I'm not "andym", which I think kind of explains why I can't get rid of the file, so we have to delete the link explicitly.
8. sudo find . -type l -delete
(This step thanks to http://www.commandlinefu.com/commands/view/2369/find-broken-symlinks-and-delete- them.)
9. ls produces no results (which is good!)
10. cd ~/.Trash
11. sudo rm -rf Tunnelblick.app
SUCCESS! And the trash is empty.