Errors in PG's files should be reported to the Errata system: errata2010_AT_pglaf.org
Not sure how that's going to help when the problems are pretty systematic?
If you feel that a text can be fixed only by a complete re-do (maybe it's missing the illustrations, the index, or whatever), feel free to download a scanset, get a copyright clearance, and have at it.
I'm doing one such right now but I'm apprehensive of the flame-fest that will ensue if one namely me actually tries to redo an old text. But, I guess I'm willing to throw my body on the fire and see what happens *next*...
Simply complaining about errors isn't useful, nor are general complaints, especially concerning older texts, such as "italics aren't shown" or "all-caps are used for italics, not underscores".
The more general problem is that texts continue to be created that are generally not readable with fidelity by many users on many different machines. Typical problem, as others have mentioned, lies in the choice HTML coding techniques used, and a preference for visual cuteness on one or another HTML machine rather than on fidelity on a wide variety of HTML and HTML derived machines -- including issues of "accessibility."