Speed up SQL Developer Startup
If you are using SQL Developer 2.x you can reduce your startup time by about 20% by disabling any unneeded extensions. I was able to reduce my startup time from 11 seconds to 8 seconds by turning off all extensions (none of which I really needed anyway).
For SQL Developer 3.x the benefits of disabling extensions are more pronounced because there are a lot more extensions supplied with the default distribution. You can reduce your startup time by up to 75% by disabling all the extra extensions. I was able to reduce my 3.0EA1 startup time from 35 seconds to 11 seconds by disabling all extensions.
You can disable extensions in the Tools/Preferences/Extensions screen. You can probably turn them all off and still have a capable tool.