4. Propping up existing monopolies in the domain of electronic communication

This problem may not be meaningful for the individual user, but it affects dramatically the community of users. By exchanging and publishing files in proprietary formats, you implicitly force your addressee to use the same software that you used for producing and storing your data. The message that is implicitly conveyed when exchanging a file in a proprietary format is "Use software X or you won't be able to read this file".
This practice - which also appears when you exchange a file in a given format by considering self-evident that any other users possess the required software - has a twofold consequence:

1. On the one hand, this practice enforces and strengthens the usage of a proprietary format owned by a company as a de facto standard∞: this means making interoperability, accessibility and perennity of your data "hostage" of the contingent policy of a software company. If the software producer decides or is forced to stop developing the software needed for interpreting a specific format, all the existing files encoded in this format will suddenly become unusable: since the format specifications are not publicly available, it will be impossible to retrieve the full content encoded in a file.
2. On the other hand, by propping up a de facto monopoly, this practice hinders fair competition between software producers - which is admittedly an essential condition for technological development - and weakens the initiatives for promoting open format specifications and public standards - which are commonly regarded as minimum guarantees for free and fair competition.