Just my point of view on this whole issue. Disclaimer: I'm a total retard with respect to patent/legal stuff, and I do not work for any company.
It seems to me that the chances of getting in 'trouble' when I would be developing on/using Mono seems to be a lot bigger than when I for example hack on my pet project libwpd. Corel here ensures me that I won't run into trouble as long as I add the following disclaimer: "Note that libwpd is not manufactured, approved, or supported by Corel Corporation or Corel Corporation Limited". I can live with that.
The day I get a letter from any big company located in Redmond related to some currently imaginary OSS project I'm working on, I'll stop hacking on it immediately. I don't have a company backing me up like Nat, Havoc and others have. Keep in mind that there are still 'stand-alone' hackers out there working on GNOME (related things). We can't afford being sued.
I want to concentrate on having fun producing (usable) code; I do not want to run into potential legal problems, and it seems to me that the Mono path is more dangerous than a project like Abiword or libwpd. If only MS would say they'd let us have our fun as long as we tell the world: "Note that Mono is not manufactured, approved, or supported by Microsoft Corporation".
Nat: Lucene itself is actually quite nice indeed. I wrote the search functionallity using Lucene for the Content Management system that ASML (the company who makes lithography systems for Intel and the like) for example is using for their website.
Just wondering: why writing all the different filters again, when we already wrote them for AbiWord? AbiWord can even be used as a file format convertion daemon (non-graphical of course): dump a document to it and let AbiWord convert it to anything you like; plain text for example, so Lucene can index it! That would give you instant indexing/search capabilities for document formats such as Microsoft Word, Corel WordPerfect (complaints to me when a documents does not convert :), superb RTF support (only MS Word itself has better support for RTF, really), and a lot more. How nice would that be?
That reminds me: I should finally put an initial AbiWord SDK in our CVS and on our homepage, so everyone can see how easy it in fact is! Maybe tonight...