I have only purchased a couple of digital comics before. I bought Darwin Cooke's adaptation of Parker, and I also got the recent Marvel version of The Wizard of Oz. They looked fine with my old nook tablet, but they looked much better with the HD+'s 9 inch screen. Still, I didn't buy any new ones, even though Barnes and Noble increased their comic book catalog and started to include individual issues for sale.
When it comes to most books, I have no problem reading them on an e-reader. In fact, for the kinds of books where I'll just read them once and then never look at again, I prefer reading them that way. I also like reading magazines like Time and National Geographic on my nook, as I don't have to deal with a stack of magazines that pile up in my bathroom.
With comics though? I guess I'm a bit of a purist. I figure that it would be nice to have access to an online catalog if I ever miss an issue. For instance, I'm missing one issue of the series Planetary and I can't find a copy of it at a reasonable price anywhere, whereas on Comixology, I can find it for less than the original cover price. While I prefer the physical books, I can live with an issue on my tablet.
I've tried reading some comics on my phone, where you need to utilize the "smart panel" technology. For those who don't know, it essentially breaks up each comics page panel by panel, so you can get a better look at it and actually get the text large enough to be legible. This involves a lot of shifting your phone around for panels that are optimal in vertical versus horizontal modes. Personally, I find that annoying, and I don't like reading a comic book that way for the same reason I don't like watching movies in "full screen". It's clearly not the artist's intent for you to view it that way. There's a certain layout that's specific to comic books, and a good artist makes use of this layout. When you break it up, you might be getting a good look at what's going on, but it feels like a different experience to me.
For me, the most promising thing is Marvel Unlimited. Essentially, it's like a Netflix for Marvel's back issues. For $10 a month, you have access to a very large selection of the publisher's catalog. I signed up for this, and while I have a couple of issues with it, I'm really digging it.
The problems are as follows: the pages don't fill up the screen of my nook. I try zooming, but to no avail. It's big enough to be legible, but I have to hold it up fairly close to my eyes. It basically shrinks it down to "digest" size. Also, while you're supposed to be able to reserve up to six comics for offline reading, that feature seems to be a bit buggy. For some reason, I'm only able to download a three-page preview of each issue. This isn't too horrible though, as I do most of my reading at home, where I'm connected to the wi-fi. Sometimes I take it to work, and we have wi-fi there now as well, so this shouldn't be too much of an issue. Lastly, you're not going to find any recent issues, as everything is at least six months old.
With that said, I still am pretty jazzed about this. There are a lot of comics out there that I want to read, but I either don't have the money to get them all. Plus, comics take up space, and sometimes I limit myself based on the simple fact that I don't want to take up any more room than I have to.
Do I think that this is going to replace my regular trips to the comic book store? Absolutely not. There will always be books for which I want the physical copies. If anything, this just means that I'm reading a lot more comics. (I signed up for it a couple of days ago, and I've read about 12 of them - which means I'm getting more than my money's worth.) There's a ton of stuff that I would most likely never buy unless I saw really cheap, but this way I get to check them out and see what's going on. For instance, I don't think that I'll ever be a regular reader of Scarlet Spider, but I'm curious enough to know what's going on in that series for me to read it this way.
I guess the real question is whether I'll eventually run out of stuff that I want to read. Will it be like Netflix which adds stuff at a faster rate than I can view them? I guess that's what is nice about a monthly subscription. Still, I'd like to see DC and some of the other comic book companies do something similar.