I've just signed up with Comixology in order to read a digital only comic. I did "download" a free one to check things up, but that's it so far. I have noticed, however, that DC has made some comics available there that have never been collected into trade, so that's a possible future purchase.
As for cost, frankly, I don't think comics cost that much. The way I usually put it, back in the 30s comics cost a dime and so did a cup of coffee. Now they cost 3 or 4 bucks, but so does a coffee flavoured drink at Starbucks.
Of course, I don't actually buy that many comics, compared to some of you. My pull list has only about 15 or 16 titles on it, and most aren't monthlies. Unless I buy a trade, my weekly bill rarely tops $20 and often its less than $10. (Again, that's not including trades.) My pull list is actually on the upswing as I am beginning to move away from the wait-for-trade mentality. I like comics.
I wish I could find the link, but I read not long ago that the vast majority of comics shops in the US were found in only four states, leaving the rest of the country severely under served. Digital is answering that need more so than replacing the LCS.