What are effective optimization techniques for Views 3? I have been doing a bit of profiling on a site I am working on which extensively uses views. 

Views takes up about 2/3 of the processing time even with the views caching on. Are there best practice ways to speed up views, or things which are known to cause performance hits. 

I should add that the views are solr views, so this is a question mostly about the views architecture rather than optimizing queries. 

Have tried using APC, but it didn't change the execution time much.
You first should find out where the performance bottleneck is.


Is it the executing of the query
Is it the rendering of the view
Is it a specific function


See http://drupalperformanceblog.com/drupal-xhprof-profiling about the article.

Once you have the problem it's possible to fix it.
You wrote that you had enabled views caching: Which kind of caching output or query cache?