I just read this article: http://news.yahoo.com/s/afp/20070806/sc_afp/britainsciencelevitation_070806132733

It says that some scientists reversed the Casimir force and were able to levitate small objects.

Personally this is surprising to me if correct. I'd never even heard of the Casimir force before.

After a little reading, apparently the Casimir force is due to virtual particles, temporarily occupying a space, which at small distances makes a consistent force? (I don't study physics so please spare me your wrath if I've screwed up). If that is right I have two questions:
1. Does this force vary by element?
2. How could someone reverse a force due to the temporary occupation of space by virtual particles?

One story ( http://news.bbc.co.uk/1/hi/scotland/edinburgh_and_east/6932283.stm) about this said that this was done by putting a lens between two objects, but without further detail.

Very few details in both articles. But, they are supposed to publish in New Journal of physics. Its open access so stay tuned:

http://www.iop.org/EJ/journal/1367-2630/1

Hi Exhumed,
You might have to wait for the real article to be published in The New Journal of Physics (http://www.iop.org/EJ/toc/1367-2630/9/8).

This site: The Casimir Force (http://www.casimir.rl.ac.uk/) says:
The main feature of the Casimir force is its strong dependence on shape, switching from attractive to repulsive as a function of the geometry and of the coupling with the constraining objects.

A Google Scholar search on repulsive casimir force (http://scholar.google.com/scholar?q=repulsive%20casimir%20force) gives a lot of links.

The authors' contact info is available here if you're really keen: St Andrews University press releases (http://www.st-andrews.ac.uk/news/Title,14834,en.html)

Beaten by bsemak :)

Right, the paper is out. I had a brief scan and it seems to be theoretical!!!!!!!!!!!!

No measurements!!! No experiments!! How dissapointing. Reading the above articles, I really thought they did some experiments. Ah well. Maybe it will come later.

http://www.iop.org/EJ/abstract/-search=27280987.1/1367-2630/9/8/254

For 276 pages on Casimir (my saved reference from 2001) See:
arXiv:quant-ph/016045 v1
It is stored in my computer, but think this correct link. If not, title and authors are:
New Developments in the Casimir Effect
M. Bordag, U. Mohideen, V.M. Mostepanenko

Abstract follows (I did not clean up the line returns and strangely omitted characters in this copy. I.e. eect=effect, eld=field etc.):

We provide a review of both new experimental and theoretical developments in the
Casimir eect. The Casimir eect results from the alteration by the boundaries of
the zero-point electromagnetic energy. Unique to the Casimir force is its strong dependence
on shape, switching from attractive to repulsive as function of the size,
geometry and topology of the boundary. Thus the Casimir force is a direct manifestation
of the boundary dependence of quantum vacuum. We discuss in depth
the general structure of the innities in the eld theory which are removed by a
combination of zeta-functional regularization and heat kernel expansion. Dierent
representations for the regularized vacuum energy are given. The Casimir energies
and forces in a number of congurations of interest to applications are calculated.
We stress the development of the Casimir force for real media including eects of
nonzero temperature, nite conductivity of the boundary metal and surface roughness.
Also the combined eect of these important factors is investigated in detail
on the basis of condensed matter physics and quantum eld theory at nonzero
temperature. The experiments on measuring the Casimir force are also reviewed,
starting rst with the older measurements and nishing with a detailed presentation
of modern precision experiments. The latter are accurately compared with the theoretical
results for real media. At the end of the review we provide the most recent
constraints on the corrections to Newtonian gravitational law and other hypothetical
long-range interactions at submillimeter range obtained from the Casimir force
measurements.

Thanks Billy