The next version of Cloud9 will use a top-level .c9 folder in the workspace for settings and metadata.

which is ".target" directory.

Those belong in other ignore files.

Based on advice in the documentation at
http://www.sublimetext.com/docs/2/projects.html

From the documentation at http://docs.vagrantup.com/v2/getting-started/project_setup.html

"The Vagrantfile is meant to be committed to version control with your project, if you use version control. This way, every person working with that project can benefit from Vagrant without any upfront work."

The old pattern was too broad and was making VIM ignore Scheme (*.scm) files.
Now it only matches files that start with . or _.

Documented at http://docs.vagrantup.com/v2/getting-started/project_setup.html

These files are created automatically the first time a vagrant box is started.

As is clearly stated in the [eclipse documentation](http://wiki.eclipse.org/FAQ_How_do_I_set_up_a_Java_project_to_share_in_a_repository%3F).  
This gitignore has lead to much confusion in SO - please ammend

I would guess the same is true for .pydevproject and .cproject but can't
be sure/do not have any references on those

Also .launch configurations are generally meant to be versioned when
saved under project location. See for instance :
http://stackoverflow.com/a/337317/281545

https://github.com/mpeltonen/sbt-idea generates this folder

.*.s[a-w][a-z] matches named swap files.
.s[a-w][a-z] matches unnamed swap files.

ignores .<filename>.kate-swp and (older version?) .swp.<filename>
see http://bit.ly/14XyBgW and http://bit.ly/chKUoZ

A lot of web designers still uses DW, thats why its necessary.

Because files and directories starting with a `.` are not ignored in general.