Now what I am really missing in Omnifocus is a possibility to "Filter by Context" while you are inside a project.

Let's say for example that I am using my Omnifocus on iPad. I am going thru various different projects and folders (in project-view) and I look at my Finance single action list. I have there 50+ different tasks inside. Suddenly I need to
see my bills ONLY inside this single action list. There is no way for me to quickly now filter by context and select @bill.

To achieve this, I have to first go away from project view to context view. Then find context @bill and then I get a list from ALL projects with a context @bill and I can go down until I find project finance, and finally get the data I am looking for.

..Not very user friendly behaviour in terms of user interface. It would be handy for example that as you are in the project view that you could use the eye-button (that changes the availability) to also define a context you want to filter with.

So I really hope that Omnigroup will add 'filter by context' possibility into the future releases of Omnifocus.