Contrary to some other answers, I think the MathOverflow archive should be as textually literal as possible, though there is no need to preserve fancy formatting, logos or any bells and whistles that are meant to make MathOverflow more pleasant to use rather than to read. I would be very happy with something very plain (such as what you see below the separation line when looking at the [revision history of a post](http://mathoverflow.net/posts/1234/revisions)).

I don't think there is any need to convert to PDF or any other format. The reasons for this are multiple. Markdown (the format MO posts are currently composed and stored in) is very compact and simple. It's perfectly readable even without markdown processing, so little is lost even if markdown goes out of fashion. Storing the math as LaTeX code is also generally better than compiling it and preserving the output. Alternately, LaTeX code could be converted to something which is standardized (such as MathML, for example) but LaTeX is pretty much a standard at this point. The only thing that might require maintenance is upgrading the character encoding from UTF to whatever comes next but that won't be a problem at all if and when it happens.

I think the archive should include comments since many do contain much substance and some posts don't make sense without them. It's true that a lot of comments are just chatter but I don't see any good reason not to preserve those too and I can't think of a good way to sift through comments. Besides, knowing that their comments will be preserved forever might make users think a lot more before posting something inappropriate.

One contentious issue is how to handle deleted material. Archives typically work only one way: you can put stuff in but you can never remove anything. I can think of two ways of handling this: (a) make deleted material unavailable but still preserved, (b) clearly mark deleted material as redacted. Maybe there is another way? (Note that the current site uses (a) for <10k users and (b) for 10k+ users.)