I must admit to having a jar of the commercial stuff in the fridge as a back up. But i would certainly not use it for cooking curries . Comes in handy when small quantities are required though, like when prepping keema kebab mince, samosa filling or onion bhajis when i haven't got any fresh.
Like Gav I now have the frozen garlic and ginger blocks in the freezer. As there's no preservative i use these all the time for convenience, just mixing up the desired ratio of each, covering any left overs with oil and keeping in the fridge. I think it was Chewy who first posted about these quite some time ago.