The comic store for the PSP was a pretty fantastic idea. I only used it a couple of times – I'm not really into comics – but from what I saw it offered a unique, interesting way of reading panels and getting access to comic books. Whether it was an enjoyable way of accessing things for an avid comic book fan, I can't tell you, but I always presumed it was a quiet success.
Unfortunately, with the switch in support to the Vita, Sony have announced that the PSP comic service will be closed in September. March 15th will be the last content update and, if you want access to your purchases, you'll need to back-up anything you want to keep on the MediaGO service.
Apparently they're looking into bringing a similar app to other Sony products (probably the Vita), but nothing concrete yet. This is an understandable closure but, on the flip side, shows a darker side to digital content – your purchases will be blocked come the end September.