Underdark lists a couple of case studies from the QGIS site, but taking your wider description of "communities" as opposed to solely government, there are many more case studies on the QGIS site worth citing. Also, check out the list of companies who support the development of QGIS. They don't sponsor it just to feel good! They sponsor QGIS because they use it, which should provide some credibility.
I can cite a couple examples from personal experience (though not US) of commercial use of QGIS.
- As a Freelance GIS Consultant I rely heavily on FOSS4G and have found that there is nothing I can't do using tools from the OSGeo stable, with QGIS at the core of the mix, that I used to do with ArcGIS (plus Spatial Analyst, Data Interoperability Suite and 3D Analyst). My clients are mostly developers working on planning applications.
- I have also recently become a subcontractor for a much larger GIS company here in Scotland called thinkWhere. I normally try to avoid anything that can be construed as advertising but the link and following quote seem appropriate in this context:
Our customers include local authorities, Government agencies and other
public sector organisations at local, regional and national levels.
Our commercial customers work across a range of sectors including
Renewables & Energy, Environment, Land & Property and Transport &
Infrastructure. Finally, our focus on Open Source solutions means that
third sector customers, including charities and Not-For-Profit
organisations, can also benefit from implementing GIS.
What is especially interesting about thinkWhere in the context of this question is that this commercial company grew out of an organisation called "Forth Valley GIS" (based in the Forth Valley in Scotland). Forth Valley GIS was originally set up many years ago as a partnership between Stirling, Clackmannanshire and Falkirk County Councils as a means of pooling their GIS budgets to improve efficiency. Back then they used ArcGIS (I don't think QGIS even existed at that time). Since becoming a fully commercial organisation however, they have adopted FOSS4G technologies and now provide training and support to enable Councils and other client make the switch from proprietary GIS software to QGIS.
Another snippet that may help your case is that QGIS makes heavy use of GDAL... and (wait for the shocking revelation)... so does ArcGIS, expect you have to pay ESRI for the privilege. Also QGIS provides an interface to GRASS - which was originally developed by the US Military before being released to the FOSS community. My point is that QGIS is built on solid, tried and tested, commercial-grade technology, a fact which should provide some comfort to your employers.
The downsides of using QGIS will be:
- a temporarily frustrating learning curve to get operators switched over to the new system (I advocate a clean break as the shortest route to gaining proficiency - who remembers switching from ArcView 3.2 to ArcGIS 8.0? It was painful but worth it.)
- no centralised telephone support, although there are increasing numbers of companies now offer this for QGIS, so maybe this isn't an issue anymore (I notice from a quick scan of the list, there is a GIS company offering QGIS support in Southeast USA in that list - though I know nothing about them). There is also an active community where you can get advice.
- making FOSS (any FOSS) work well together usually requires a higher level of technical ability for at least some members of the team than with proprietary software.
- wondering what to do with the money your employer will save...