debug on!

[szepeviktor]

Please develop with debug on.
And I suggest you to use TravisCI. There are prefessional plugin repos using Travis where you can steal code.

Using daily backup with no subdirs, saving changes:

Notice: Undefined index: day in wordpress-backup-to-dropbox/Views/wpb2d-options.php on line 49

Notice: Undefined index: store_in_subfolder in wordpress-backup-to-dropbox/Views/wpb2d-options.php on line 50

[szepeviktor]

I do like your conditional loading
https://github.com/michaeldewildt/wordpress-backup-to-dropbox/blob/master/wp-backup-to-dropbox.php#L31-L54
This plugin shows you what is running
http://wordpress.org/plugins/whats-running/
And you can test these entry points:
https://github.com/szepeviktor/WPHW/blob/master/wp-entry-points.md

[szepeviktor]

Some code styling guidelines: https://github.com/WordPress-Coding-Standards/WordPress-Coding-Standards
And a handy tool to do it: https://github.com/scribu/wp-phptidy