The depth-of-field is not solely determined by the aperture width (F stop) but also by the Focal Length. I believe your friend digicam has a very short focal length, that's why he/she cannot get a shallow DOF effect at F2.8.
Like what skf said, those are the 3 rules to remember. In addition, most digital P&S will never get good background blur. For example, the G1 has a focal length of 7-21 mm (equivalent to 35-105 in 35mm). Even at f/2.8 at the longest, your background will never be nicely blurred out.
Actual aperture size = focal length / f-stop value
hence the notation f/2.8, f/5.6 etc. Comparing a lens with, say 15mm and a lens with 150mm, with the same f-stop value, the 15mm will have a much smaller actual aperture opening which would result in deeper DOF.
In the case of digital camera, eg. the G1, since the lens is 7-21mm, at 21mm (105mm equivalent at 35mm) its aperture opening is still much smaller then its 35mm equivalent at the same f-stop, resulting in the deeper DOF.
so a 50mm prime lens can achieve shorter DOF than a 35mm one...in general..rite? also a faster lens will give shorter DOF at its max aperture as compare to a slower one at the same focal length....rite?