I know that I can do this if I open a text file and use Xcode but often when working on a project, I want to have a temporary place to write something (usually stuff that I'll be copying into the Terminal). Any way to do this in Xcode 4.3?
There is no a way to do this in Xcode. It must be related to the project or workspace. It even does this if you deselect the target.
It sounds like what you need is a text editor and not an IDE like XCode since XCode is built for OS X and iOS development primarily. You may want to try TextWrangle for free, or it's purchasable counter part BBEdit.
If your doing C/C++, Python or PHP work, you may want to try some of the other JetBrains products like AppCode, PyCharm or PHPStorm. There is also Eclipse, with it's many plugins, the heavy favorite amongst many developers.
Specific to RoR, rvm 1.9.3 works with Xcode 4.3.2. Issue was fixed 16 days ago. See https://github.com/wayneeseguin/rvm/issues/846
For other tools, install the "Command Line Tools" option under Components in Xcode, and you're ready to compile native binaries.
One suggestion, file a rdar at bugreport.apple.com to request php, ruby, python templates be re-included in Xcode. And please remember to file a copy of the rdar at http://openradar.appspot.com/page/1 so rest of us can also file our own rdar referencing your rdar. This helps escalate it to the attention of Apple Engineers.
Lastly, post the details of your openradar filing here so future readers can also do the same. Thanks.