At the 33rd LPSC conference in March will be presented a report suggesting small liquid carved rills are currently forming on Mars:

SPRING DEFROSTING IN THE RUSSELL CRATER DUNE FIELD - RECENT SURFACE RUNOFF WITHIN THE LAST MARTIAN YEAR ?
http://www.lpi.usra.edu/meetings/lpsc2002/pdf/2013.pdf

The authors reference an image discussed on this group showing many small apparent rivulets in Russell crater:

Dune field monitoring
http://ida.wr.usgs.gov/html/m19011/m1901170.html

Perhaps someone will post the link to the discussion on this bbs on this image.

The authors of the report make a distinction between "gullies" and "rills" based on the rills arising from surface flow and the larger gullies requiring subsurface flow. Some reports on the Malin/Edgett observed flows do suggest though they stem largely from surface melting and flow:

Session 51: MARTIAN GULLIES AND MASS FLOW
Lunar and Planetary Science XXXIII (2002).
http://www.lpi.usra.edu/meetings/lpsc2002/pdf/sess51.pdf

The authors of the "SPRING DEFROSTING IN THE RUSSELL CRATER" report suggest these rills are formed by melting liquid water and give TES temperature measurements of this location that show above 0 temperatures can be reached to support their argument.
Nick also argues that the gullies are currently forming but suggests CO2 flows for their origin:

Near-Polar Channels on Mars
Water or CO2?
http://irian.geology.latrobe.edu.au/~nhoffman/Mars/Polar.html

Annotated example
http://irian.geology.latrobe.edu.au/~nhoffman/Mars/Explain.html

If these flows form annually further MGS imaging at these sites may be able to provide before and after images of the flows.

In regards to the flows being caused by liquid water under the low atmospheric pressure on Mars I found a report discussing experimental evidence that this could indeed occur:

Martian Outflow Channel Formation by Water Erosion Under Nonequilibrium Conditions
Abstracts of the Lunar and Planetary Science Conference, volume 20, page 666, (1989)
http://adsabs.harvard.edu/cgi-bin/bib_query1989LPI....20..666M [full text]

Wallace and Sagan have also argued that protection by an ice cover may have allowed liquid water to carve channels even under present Martian conditions:

Evaporation of Ice-Choked Rivers: Application to Martian Channels.
Bulletin of the American Astronomical Society, Vol. 9, p.539.
"The evaporation rate of water and ice under present martian conditions has been calculated, and is sufficiently low that at least some Martian channels may have been formed by flowing water even with an atmospheric pressure as low as the present value. While liquid water does evaporate quite rapidly, the evaporative cooling causes a layer of ice to form on top of the water and greatly reduces further evaporation."
http://adsabs.harvard.edu/cgi-bin/bib_query?1977BAAS....9..539W [full text]

Evaporation of ice in planetary atmospheres - Ice-covered rivers on Mars
Icarus, vol. 39, Sept. 1979, p. 385-400.
http://adsabs.harvard.edu/cgi-bin/bib_query?1979Icar...39..385W [abstract]

Bob Clark