How about explaining/exploring issues around extreme movements/
fluctuations in SERPs results for some keywords and some sites that
occur over short timespans.

For example, we frequently get questions along the lines of: My
website is on SERPs page 1 for <keyword> every other week. On
alternate weeks (or at weekends etc) it dives to about 300th position
and then returns to Page 1 the following week.

Rationale: Forum regular members can usually give quite detailed and
hopefully insightful comments/feedback about many website indexing/
ranking issues such as crawlability, redirection, use of head titles,
header tags, Toolbar PR, hidden text, keyword stuffing, content-
duplication, etc etc.  However, there seems to be little clarity when
responding to queries about oscillations/fluctuations in the SERPs
over short time periods.  We cannot even see independent evidence that
what the webmaster is claiming is in fact true.

So I think it would be helpful if Google staff experts could focus on
the mysterious area of short-term oscillations/fluctuations.   Is
there hard evidence that this phenomenon does occur?  What causes it?
What can webmasters do to mitigate it or avoid it altogether?    Is
the "problem" on the site itself?  Or is it to do with the way
indexing algorithms interact and revisions to ratings?  Why do some
sites allegedly experience this sort of thing repeatedly while others
have very steady positionings (including long term rises and long term
falls)?

Robbo