In one of my earlier logs I proposed monitoring power usage of the machines, but after some research I've found that this is not a practical option (at least in Denmark where I am based). Current transformers, such as SCT-013-000 proposed by Gregor and similar models I've found all require that you break the outer insulation of your wire to expose the live or neutral wire. In Denmark (and I presume plenty other contries?) it is a legal requirement to have two layers of insulation on your wire, meaning such exposure is illegal.
If the clip went around the insulated wire then I'd consider it unobtrusive and it would be legal. This type of installation won't do. Picture by Calypso_rae https://openenergymonitor.org/emon/node/870
A practical solution to this could be to make a box in which the wires are exposed and the sensor mounted. The box would provide the second layer of insulation, making it a legal installation. However, personally I think this is to cumbersome and legally sketchy (and potentially really dangerous) to be a practical approach for this project, when the accelerometer data so far is really promising.
Another approach could be to hack a watt-meter, as seen here from the wattmote project, link below
Another option could be to buy a watt-meter, like Kill A Watt or similar but this falls into the same bucket as monitoring e.g. the lights on the washing machine. Different meters are likely to behave differently and I can't expect the same meters to be available to everyone, so it will be hard to make a general solution. Also, I think it might be even hard to hack a meter than to use a current transformer sensor. For examples of such projects see http://lowpowerlab.com/blog/2012/12/28/wattmote-moteino-based-wireless-killawatt/ and https://learn.adafruit.com/tweet-a-watt/.
I might have overlooked options, be misinformed or otherwise mistaken. Please let me know in the comments if so :)