JManga
If you were thinking of checking out JManga, now's the time to do it! They're having a sale, continued over from October, where they are slashing prices by up to 60% off, which means that an $8.99 volume of manga now costs $4.99, which is much more reasonable for a digital copy that you can only read online while logged into their site. (At this time, you are unable to download a file to save on your computer or e-book reader.)
I signed up for a subscription and have bought several volumes myself. The manga reader is similar to Viz's, and works pretty well--it's a better size and is easier on the eyes than the Kindle app, and does have a zoom feature. And JManga offers many interesting titles that are not available anywhere else in English, such as Ekiben Hitoritabi, which is about a guy traveling by train around Japan so that he can indulge his love for both trains and train station bentos. (This should appeal to fans of Oishinbo, but be warned that reading this manga will make you very hungry!)
Things I don't like about JManga: (1) you have to sign up for a subscription before you can purchase anything. It costs $10 per month, and the $10 is converted into 1000 points for purchase, and they throw in an extra 500 points when you first sign up. (There's also a $25 subscription fee that gets you more free points.) You can covert back to a "free" membership at any time, and you'll still be able to access the manga you bought previously, but the subscription thing irks me a bit. Why can't I just buy stuff when I want without having to subscribe?
(2) I really dislike the points system. The way JManga works is that you buy "points" to purchase manga--the points from your subscription fee, and you can buy additional points in increments of 5, 10, and 25 dollars. At present, the store is only accessible by US customers, but I've heard that the points system is probably to make it easier to expand into foreign markets--instead of having to convert, say, yen into dollars, a Japanese customer could just purchase the necessary amount of points to buy a manga.
(3) Except that a volume of manga costs $8.99 (or $4.99 on sale), and since you can only purchase points in 500, 1000, or 2500 increments, that means you will always have leftover points, since it's almost impossible to make a purchase come out evenly. (This is also why I've avoided using the emanga site, btw.) Unused points roll over to the next month, but expire 1 year after purchase. (Which is another sore point with most JManga customers.)
(4) There are also a lot of manga titles listed on the site that aren't available for purchase. I'm assuming that they will be eventually, but it is a bit frustrating to get all excited about seeing a title you want to buy, and then finding out that you can't buy it. It's fine if they want to promote upcoming titles, but they should make separate categories for titles that are available and ones that are "coming soon" (or "at some indefinite time," since there are no release dates listed).
So with these misgivings, why am I still a JManga customer? They have a lot of interesting titles that are probably too niche to be picked up by print US manga publishers like Viz. And they have Youka Nitta and Matsuri Akino titles listed in the "not yet available" non-category, and I'm holding out hope that I'll eventually be able to purchase them. And finally, from what the various manga bloggers have been reporting, JManga has been receptive to reader feedback. The current sale is a good sign, since people have been complaining that their prices were too high. I'd like the price decrease to become permanent, since I probably wouldn't buy many of their titles at full price unless I actually get a copy I can download and read offline. But since they're a new business and seem to be listening to their customers, I'll give them a chance, and wait and see if they can iron out the kinks in the system, so to speak.
