I think it's a great way to help "pay" for your machine.
I've been hoping that some LQS' would rent it, as they do with LAs.
It sits idle when you are not piecing, so I've always thought it'd be a great machine for two friends to own together, where they could go to each others homes to use it; and/or that it "lived" in each home for three months (for example) and moved to the other for the next three.
Some things to consider --
* liability, as mentioned above; speak with your insurer and discuss
* do you want other people in your home?
* how will you handle things, if there are problems with the machine while someone else is using it?
* are you prepared to teach FMQing? many who rent may not have the skills and will look to you to take them thru it all step by step
* would it be easier on you to take in custom quilting, instead of renting the machine?