Application frameworks such as DotNetNuke, Eclipse, Websphere and so forth are available today which offer customizable frameworks that can be used as dashboard applications. Do you use these or do you and your peers keep writing amazing, modular, maintainable dashboard frameworks which you support yourselves?
Are there any good web based, OS independent frameworks out there that you suggest using to build your own enterprise class infrastructure around?
The one I use is Oracle Application Development Framework. It's a complete, fully supported framework, and Oracle use it themselves to build their own enterprise applications. It comes with a lot of JSF components that are very easy to bind to the underlying data objects. I'd recommend this for all Java applications that need database data.
You find a discussion of it on the Oracle Wiki: http://wiki.oracle.com/page/ADF+Methodology+-+Work+in+Progressent
There's no one right answer. Look at the business need... if you're doing fairly typical things, then starting from an established framework is a good place to start. If you feel you may need some custom components or widgets, look for a framework that's extensible using the knowledge and skills that you have in-house.
Unless your line of business is to build application frameworks or dashboards, one should look very hard before building a whole new framework or dashboard.
At work, we try to create from scratch as little as possible. We use Frameworks a lot (maybe not always end to end frameworks). We have used Dot Net Nuke a lot. Another framework we use a lot is CSLA.
I personally use DotNetNuke quite extensively for both personal and business related ventures. However DNN does not meet one of your requirements as it is a .NET solution so it is windows dependent.
I have found that using DotNetNuke has greatly reduced our time to delivery, and we can focus on our core needs rather than the implementation of the common pieces.
Be careful to consider how scalable the framework is. There are several frameworks out there that like to hammer your database because they think it's nothing but a glorified file system... those frameworks don't scale well at all.