Have the bar represent the number of new comics
The bar beneath each comic title on the front page currently represents what percentage of the run I've read. This is marginally useful information when I'm reading an archive, but it's more important to know if I have 1000 or 10 to go rather than whether I'm 10% or 90% of the way through. When I'm caught up, it's totally useless information.
How many comics are unread is useful information for both situations.
Kelsey Higham commented
What I think this suggestion is asking for (and what I'd like to see) is the EXACT NUMBER of pages left. Right now, you can perform subtraction to figure out how many pages you have to go, but isn't it much easier to read "23" than it is to calculate 691-668? Especially if you're trying to access that number a lot — like if you're trying to determine whether you have enough time to finish the archives before class/lunch/work/chores/bedtime/whatever.
What I'd recommend is to copy iTunes's way of doing things — show the number of pages you've read (668) on the left, and the number of pages to go (23) on the right. Those two numbers are much more useful than the total number of pages in most cases; and if you really need to know how many pages Bobwhite has, you can add the two (691). (Or display that number elsewhere. You're already displaying "1" on every page.)
AdminJosh Triplett (Admin, Comic Rocket) commented
The text next to the progress bar already tells you precisely how many pages you've read out of the total, and thus how many you have left to go. (During the prototyping of this new design, those numbers changed from a percentage to specific page counts to address precisely the concern you mention.) The progress bar tries to provide a separate visual indicator of how much of the comic you've read.
In general, a progress bar shows percentage of a total; if it showed the number of new pages as you suggest, what would it show that as a percentage of? (I don't think "percentage of all new pages" makes sense, because it'll become massively skewed the moment you get behind on a comic or start reading a new comic with a large archive.)
What information do you want to see that you don't currently see?
Also note that the entire block tries to provide a consistent look and UI for both your user page and comics shown when browsing or searching; in that context, it helps to see at a glance if you read a comic and how much of it you've read. (At the moment your reading progress doesn't actually show up when browsing or searching; that needs fixing.)