I think it's great and impressive that you can install and run two versions simultaneously, but I have found a couple gotchas in the process. Maybe those are documented somewhere, but if so I haven't seen it. The issues I hit all had fairly easy solutions, but I'd humbly suggest that a "things to watch out for when running multiple versions of Postgres concurrently" might be a useful document.
You can always add something to the wiki. It's going to be distribution specific which makes adding it to the docs less desirable.
