It's one thing for a private party to own your software, but the files you create with it should be your own.

Agreed, and now with the DMCA in place it's questionable whether or not one still has the legal rights to reverse engineer the proprietary formats of one's own files.

It's not surprising that Massachusetts made the move that it did (or that Texas is now considering something similar).

One thing that has always irked me about PC software (and much Mac software too) is this model where only 1 program can process a certain type of file. I want different programs to be able to do different things with the same file, in traditional Unix fashion. That's why I like to make my data files text files instead of binary.

Macs have gotten better over the years in that regard.  They've honestly put in an effort to use reasonable XML (not just binary blobs encrypted within XML outer layers).  Furthermore, the word on the street is that they'll be natively supporting the various OpenDocument formats with their next release of OS / iWork.  Plus, one of my favorite data sharing models of all time was developed by Apple originally -- Newton soups. Granted, it seems like they forgot how to apply them for a decade, but some of the OS X software seems to be slowly starting to move along in that direction again.

In fairness to Macs, WinTel boxes, and UNIX machines, though, it should really be noted that file formats are as much in the hands of the app developers as they are in the hands of the OS developers.  Adobe FrameMaker has just as much a proprietary native format under UNIX as it does under the Mac or WinTel, even though UNIX -> Mac -> WinTel kind of run the gamut in their respective ratios of open system formats to closed ones.  (Although it should be noted that FrameMaker's MIF format is open.)

To express my own bias here, I currently use a UNIX desktop and a Mac laptop.  I did MS-Windows development though for a few years...

(By the way, that also makes for smaller, more efficient programs, instead of bloatware that takes forever to load.)

True enough.

XML is great. A human can read it and almost all programming languages these days have special XML libraries.

It is indeed a fine thing so long as people adhere to its spirit.  I'm a little worried because MS lately seems to be trying to use XML as a buzzword but seem to be missing the point with their latest offerings.

What do you think of the overhead of text formats such as XML?

It depends on how you mean.  For file interchange, I've no problem with it.  For content negotiations, I have no problem with it (or even RDF applications built on top of XML with even additional overhead).

For quick real-time message exchange, JSON is probably a better match, and it also has either built-in support or library support in most languages.

(P.S. I use NeoOffice at home.)

I tend to use a mixture of things ranging from FrameMaker to Pages to NeoOffice to AbiWord.  NeoOffice keeps getting better with each release, though, and I'd love to be able to eliminate my dependency on FrameMaker.