It would be nice if anonymous users (non-logged in users) could be able to define a basic set of preferences. This option is available on many websites, like search engines or encyclopedias (see for example http://www.google.com/preferences or http://www.eol.org/taxa/settings).
I see at least two preferences that would be very useful:
- Interface language
This would be particularly useful on multilingual wikis (e.g. commons:) or on wikis where the registration is required or restricted (e.g. wikimedia:).
It is possible to change the interface language by adding "?uselang=code" to the end of the URL, but it is not very practical to do this several times in a row.
- Stable versions (Flagged revisions)
If a wiki community chooses to display stable versions by default, readers or anonymous contributors should be able to choose to see current versions by default.
Draft versions can be displayed on a per page basis, but it would be much convenient to set this just once.