I recently have purchased some air tools since I acquired a 60 Gal 7.5 HP air compressor at an estate sale. Air tools are very handy when working on cars and air impact wrenches make taking off lug nuts much faster.
I have to disagree with Larry on one point. A small compressor (with low CFM output) will struggle to break loose a nut torqued to more than 120 Ft lbs. I tried to break loose my harmonic balancer bolt using my neighbors pancake compressor. After 5 sec. of continuous use the air from the tank was depleated and could not supply enough CFM to operate the impact wrench.
Concerning your original question about electric impact wrenches. I believe that the latest trend is cordless electric impact wrenches. I do not have any info on them.
1998 Mercedes E320, 200K Miles
2001 Acura 3.2TL, 178K Miles
1992 Chevy Astro, 205K Miles