I used to use textmate (w/ default plugins) for HTML, CSS, Javascript and Ruby. Now I discovered IntelliJ does stuff really fast and works.
IDEs/Editors have macros help you perform repeating work fast.
TextMate allows you to run shell commands inside the editor which is pretty useful. There are few for Ruby if you want to see output of an execution as a comment (see Avdi's screencasts).
There are shortcuts for performing tasks. In case your IDE does not provide, use the ones which your operating system supports. Example for Mac OS X - you can use Apple Scripts, Alfred, Keyboard Maestro etc.,).
Take time reading your IDE manual or help. Graphical UIs show tips and suggestions. console based provide tutorials when you open without arguments. With vi, use :help and follow the article. It takes months or even years to understand and learn your IDE.
Talking about downsides, once you start using your IDE a lot, you will learn about the downsides like 'pinky finger problem on emacs' (Google for this), and then you'll realize you have to customize your IDE. Note: These are good to have problems because you realize you are advancing.
For HTML, ZenCoding as a plugin came out 3-4 years ago where you can use div.container>div.hello+div.details>span>a*3 (on tab) will expand and give you html.
StackOverflow has lots of answers and details on discovery of productivity tools.