Sony's shutting down the PSP Comic Store on Oct. 30, so if you don't get around to backing up your comics some time in the next month, you might lose them forever. Once the store goes down you won't be able to re-download them should anything happen, so you'd be wise to use Sony's Media Go software to back them up.
The PSP Comic Store apparently hasn't been updated since July 2011, so that more astute among you may have seen this coming. Did you ever buy comics on your PSP?