I haven't done enough research to know how much of an impact it has on sales if a book is delayed or not, I can only gage my personal level of interest in whether delays impact a book or not. But as a fan almost all publishing delays hurt my enjoyment of a book. It matters more with some stories then it does for others. Ultimately books published on time keeps fans happier and sale better short term (I believe).
All Star Batman has to be the biggest joke of the delayed books. We saw one issue of this title in 2006. First off the whole story by Frank Miller is like a bizzaro version of Batman. When the book first was coming out I thought that maybe Frank was showing us that Batman without a Robin to temper him was becoming almost psychotic. With the lengthy delays who even cares about this book. With all the flaws this comic has it could have been a sales winner if the 6-12 issues they were doing with this story come out in a timely fashion. Now I could care less about the series and will be very leery of the next team on All Star Batman. This was a horrible launch of a separate line of books.
All Star Superman has been longer then every two months, but this has been a high quality story and beautiful artwork. This book is worth the wait and since it has actually come out at least quarterly it has been well worth it. This should have been the book to launch the line and can survive long gaps between issues.
Ultimates Volume 1 was so ridiculous that by the end of the series I had almost forgotten about the book. I picked up the deluxe format that collected all 12 issues and have ignored Volume 2 totally. In listening to other show panelists they seem to be enjoying this Volume, but it has lost a lot of steam in hearing them talk about it. I would have signed up for the monthly if I thought it would actually be published on a reasonable schedule. Now they added a 13th issue for Volume 2 to drag it out even longer. No point in following this book anymore. I will got the deluxe format book so I can read the story in one or two sittings.
Planetary has taken years and years to publish 27 issues, but this book is a total exception to any rules on delayed comics. I will buy the single issues and the Absolute when Volume 2 is solicited. This is Ellis' best comic work and Cassady's best art and I don't mind waiting months for their schedules to open up enough to let them do an issue. Planetary is just that good.
Watchmen was late, Camelot 3000 was late and all of the above stuff has been late. I think the lateness on these books hurts their sales, but the bottom line is the actual quality of the story will tell the tale about if these books will succeed in the long run. Where the delays I think have a bigger impact are the "in continuity stories" and especially the event stories.
Civil War is the proverbial 500 pound gorilla when it comes to this type of delay. The delays on this book have in my mind been inexcusable. This is not a separate story unto itself, it is an event book that builds with its immediacy. All of the delays have made this story fell like a strung out boring story. The bang will have to be huge for me to care about the ending at this point. If I was on a limited budget I would have dropped this book by now and moved onto something else.
Using TV as an analogy, 24 is the only TV show that I will watch anymore when it is broadcast. That is because once they start it every Monday night at 9PM I can turn on my local Fox channel and see a new episode until it is over - guaranteed, no delays, no gaps waiting for the right sweeps week, it's on Monday night. Now for Lost I get the DVDs.
Comics are getting to be the same way, get the trade or the hard cover. Like a DVD, no ads, no waiting for the story to be completed or indeterminable delays between issues or episodes.
The danger is that if I went all trade that I may not try many newer series, also I may drop off something because my interest waned over six months. It is a whole new marketing game.
Publishing delays have to be balanced out between what the project being delayed is, who are the creators and what else is being effected by the delay.
My final proof that hitting your publishing schedule on time is important for sales is 52. A series that does not star any of the major DCU characters is outselling every other DC comic and the vast majority of the Marvel titles.