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Concerns about inherited license terms from Google Web Toolkit
Vaadin is dependent on Google Web Toolkit, which appears to in-turn depend on ~8 bundled software packages (see the bottom of the page http://code.google.com/webtoolkit/terms.html). I am not well-acquainted with the various open-source licenses, and found the ones I did investigate rather difficult to parse. Put simply, must one distribute source along with a deployed Vaadin project? The Apache license does not seem to require this, but the additional dependencies give me some pause (particularly those under the LGPL).
Naturally, posters are not legally liable for any advice they provide. As a recent college grad, I can't really afford legal counsel.
LGPL is not viral - GPL is. Vaadin package do not contain or require any GPL:led code. The packages you are referring to (WebKit and JFreeChart) are both optional and safe to be used in enterprise (legal) environment. LGPL means here that is you want to modify JFreeChart of WebKit, you must distribute those modifications. When using Vaadin for your development - modifications to those packages are not required.
As a summary - you can use Vaadin without distributing your source code. No code within Vaadin package causes restrictions on how you are distributing your application. Thus Vaadin is 100% save to be used in corporate environment.
For more information, see http://vaadin.com/license
You can take the above as an official statement by IT Mill (I am the CEO)