I've even turned to bittorrenting some of my all-time favorite books just to have a "digital back-up"...the main one being the complete Micronauts books (the real ones...the ones from Marvel...not that Image/Devil's Due crap!).
But, I've also used it to read books that I couldn't wait to read...I read the last issue of "Identity Crisis" that way and also the "Countdown to Infinity Crisis" ('cause I generally get my books on the weekend)...but I didn't want to accidentally stumble across any spoilers in the meanwhile, so I went ahead and read them the day they came out (of course, I've since bought them out of my pull-box).
I've occasionally grabbed a run of a book to try it and if I like it I'll be caught up and can either start buying from the next issue or will know that I'll want to invest in the trade paperback (or not)...I tried the first few issues of "Fallen Angel" this way and am glad I didn't buy the book.
I happened to see an "Infinity Crisis" setup download that included a lot of the books that tied in to "Identity Crisis". The only books that I didn't normally read were this year's Superman books and the Adam Strange mini-series. I had planned to buy the Adam Strange books when they were collected and I've since read the first couple of issues (yesterday, finally) and YES I can't wait until this is collected into a trade.
However, now that I've read the Jim Azzarello/Jim Lee book (Superman issues #204 -215)...though the art is phenomenal, the story left me kind of empty. I'm glad I saved the $30.00, 'cause I'm not planning on even saving this one on a disc. -- OH, look...there's the delete button!