Keep in mind that you need:
- to send several mails (amount depends on the length of the key) to the victim which you know the content off, mainly because of the bandwith of the used frequency.
- a victim using an old GPG version (2.x is not affected)
- to be able to get that close to your victim at the moment the prepared mails are encrypted
- a victim using specific hardware (as far as I understood the paper not every cpu, board etc. is affected)
so keep your panties on and update GPG, which you should have done allready anyway.
And which is also quite rare (clarifying number one on your list), the recipient has to have configured her system so that it automatically decrypts any received messages. But anyway, that was just a demonstration of the possibility of such things and a very neat one. Who knows what might be possible if government agencies point sufficient resources, probably a lot more. Remember how many cryptographers NSA has employed, many of them on par with Shamir et al.
That's one crazy attack! These hardware-based attacks are interesting to me.