Comixology just launched an all you can read [of a very limited selection of titles] subscription service. I signed up for the free trial so I could look at what was being offered. Honestly it doesn’t seem to be very much to me. The top two publishers, Marvel and DC are not included in their offerings.
The have some popular titles from Dynamite, IDW, Image and Oni Press, but most of them were things I’ve picked up in bundles that I already own copies of. They have a few manga titles but no Shoujo titles that I could see or Romance titles from Harlequin Publishing. The only thing I saw that I was somewhat interested in were the Archie Comics.
Personally at $5.99 a month it probably isn’t worth it to me personally. That might change if they improve their selection of titles to include more of what I like. Might be good if you like independent comics, but I think that Scribd has a better selection of comics if they haven’t dropped them anyway.