Disable mark occurrences
Open preferences (choose of project wide or global wide preferences is up to you) window and type "mark occurrences" in filter text box. Select the "Mark Occurrences" from the list box and remove the tick from "Mark occurrences of the selected element in the current file" check box.
Remove structured text validation
This time type "validation" into the filter text box in preferences window and select "Validation" from the list box. You' ll see some of file types that are promised to be validated. Deselect validation ticks from all of the file types in the list (you can do it manually later if you want to). You'll see a really very big difference in eclipse performance if you have big xml and wsdl files. For a example in my last J2EE project, my web.xml files contain 1400 and wsdl files contain thousands lines of text so eclipse couldn't handle all the validations while computer memory is avarage
Do not use subclipse plug-in
Subclipse consumes so much system resources and effects eclipse performance greedily in big projects. If you could, consider not to use subclipse especially in projects that contain thousands of code kept in subversion source repository. It's really become a very heavy-weight plug-in with heavy-weight code. You should feel better using subversion from the command line or from a seperate client
Consider converting your static code to a jar library
This advise can be possible more likely when you have static code automatically generated from static wsdl belongs to a web service. By this way you reduce the raw code size in project and use the code functionality from compiled classes to force eclipse to use fewer system resource.
Configure java virtual machine memory management start up arguments
In your eclipse.ini file, set -Xms40m and -Xmx256m args as your needs. This options define minimum and maximum memory usage bounds which passed to java virtual machine to manage eclipse application domain's memory allocation tolerance. You can tweak this values and experiment your optimum eclipse speed. Also if you have problems in eclipse's memory management in Linux os environments like having lots of out of memory errors, you should define permgen space argument in eclipse.ini file. Setting this arguments as needed, you will have very few (or not) sudden memory exceptions. Try these -XX:PermSize=128m -XX:MaxPermSize=128m values if you got for about 1GB ram in your machine.