1. By saying XSL FO is a recommendation is the W3C putting its stamp of approval on it or is there still a higher level of approval this specification can receive?
Not that I know. It took W3 long enough (more than 2years?!) until XSL-FO became a recommendation.
2. How many (major?) vendors are actively developing solutions for this standard?
IBM is using XSL-FO in some projects. IBM also created a XSL Renderer at alphaworks. See the links in this email.
3. What other XSL FO formatters are there? I have heard of XEP, are there others? How do they compare with FOP?
http://users.ox.ac.uk/~rahtz/passivetex/ based upon TeX
http://www.alphaworks.ibm.com/aw.nsf/FAQs/xfc alphaWorks: IBM XSL Formatting Objects Composer
4. Are there many XSL FO authoring tools?
I am currently aware of two tools: http://foa.sourceforge.net/ open source, support for most formatting elements
http://www.xslfast.com/ Wysiwyg editor, commercial
5. How is Apache supporting FOP? How will this change in the future?
What I really want to know is...
Has anyone else been through a similar evaluation process that wants to
share their experience with me?
I think there are many companies out there how use XSL-FO for professional reporting. Look at the FOP mail archives: several companies described what they did with the FOP.
Stephan Albers jCatalog Software AG