CROUPIER49  Maybe I'm crazy, but how is this any different than simply typing Command + Option +D? Whenever I type this, the dock completely disappears and doesn't return until I type the command again.   
(Version 1.0b4)

CROUPIER49  Version 2.1b is a beta version. The developer's website clearly states the version is beta and notes there may be some bugs since it's still being tested. The site suggests you use the most stable released version (instead of the beta version) if you don't want to be part of testing or experience bugs. I use the most current released version (not this beta version) and have had ZERO problems. It's very handy and well-maintained. Yes, you can use a lot of free apps and browser add-ons to get similar (though not all) features as Mailplane, but they don't look or work as nicely.

  
(Version 2.1b)