Beekster wrote:Sure, a standard that has the same portability and consistency, as well as being editable would be nice. I'm sure it will happen.
It's already happened: plain text. Works perfectly for me.

I know, I know, that's not what you meant, you want formatting, and I'm just being a bit flippant. Nevertheless, it's not untrue, even if you want complex formatting, and it's already been mentioned here: my LaTeX files (plain text) produce gorgeous output wherever I compile them.
To the PDF question: indeed, the saving of filled-out PDF forms is a problem -- I don't know of any program other than the full Acrobat that allows easy editing of PDF files. And, as Beekster mentioned, the beauty of PDF over other formats is its portability: complex documents can be easily transferred without formatting loss, especially since just about everyone has acroread or an equivalent on their machines by now (can't say that about LaTeX!). As for it PDF and open standards,
PDF is an open standard. Adobe publishes the specs, at least partly "to encourage the development of third-party applications." What we're running into here is not the lack of an open standard, but that there just isn't editing software other than Acrobat (yet).
HeadHolio, here's one possible workaround to the problem: save the filled-out form as another PDF. This is trivial in OS X, which has 'save as pdf' in every print dialog, but also easy in Windows (with pdfcreator or similar) and Linux (save as ps, convert to PDF with ps2pdf). The shortcoming of this technique is that the thus-saved form will no longer be a form, and so no longer editable (i.e., you'll have to fill out the whole form at once), but it's still a useful way to keep track of what was filled in.