Well, if you're truly not using it, you could delete the instance and not be billed, then redploy when you need it.

They introduced hourly billing like a week ago :)

As long as you have a Linode provisioned, you'll be charged for it even if you're not using it. The hourly billing is just a simplification of their old system, where they would charge a prorated amount when a server is created based on how far into the month you are and issue a credit when a server is deleted based on how far from the end of the month you are. The net financial impact for a given server setup is about the same (+/- a few hours' worth of usage).

(Just to be clear, Digital Ocean works the same way. They're charging you for the resource allocation and associated maintenance. If you choose to not actually use the allocation you're paying for, that's your business.)

Oh darn, Rackspace has the same problem. I hoped it would be like AWS, where you pay for storage on S3 when not using, and hourly running costs when it is.