As background: most ebooks available for libraries are through Overdrive. (There are alternatives. Libraries can purchase devices and check the devices out loaded up with one more ebooks, thus getting unlimited numbers of checkouts out of the ebooks.). Overdrive has a policy of supporting whatever business model publishers request. HarperCollins has requested a 26 checkout limit.
With pbooks, libraries which expect heavy circulation buy multiple copies of a given book (say, _The Da Vinci Code_). After a few months or years, when circulation drops to a lower rate, the more heavily worn copies (perhaps all) will be weeded and a smaller number kept until the librarian(s) conclude(s) it no longer makes sense to keep it in the collection. eBooks don't have to be weeded and they don't wear out -- unless HarperCollins "makes" them wear out.
I think what happened is that HarperCollins looked at their most popular books and their rate of circulation and how many copies were available in any given library to support that circulation. They probably picked 26 checkouts because that struck them as really generous (assuming a 2 week checkout period, they were allowing for a solid year of use, 18 months with a 3 week checkout period, longer if there are any gaps in time when it isn't checked out and let me tell you, for most books in most libraries, those gaps are plentiful and long. I don't think Overdrive supports a longer than 21 day checkout limit but I could be wrong.).
Here's the problem: if a library wants something in its "permanent collection" and it doesn't circulate heavily, 26 checkouts is problematic -- especially if, two decades from now when nearing the end of the license, the book is no longer available for sale. So while the policy probably makes really good sense for books which are heavily circulated (and libraries would have had to buy multiple pcopies of anyway), and is not unreasonable for crappy fiction that's going to be weeded in five years no matter what, it creates a completely impossible situation for books that a librarian would want in the "permanent collection". At least I _think_ that's where the nut is. I kind of think this is chump change compared to the bad-paper problem we had for much of the 20th century (those books self-destructed in a comparable time frame).
Should HarperCollins _care_ about librarians who want to curate books? Well, this is one of those sociocultural reputation/prestige things. HarperCollins made a reasonable business decision (this is, after all, a trade press). A bunch of librarians across the country are responding in a way that makes sense: identify the source of the problem and apply what pressure you can to modify their position so the problem goes away. Should you sign the petition? I don't think it'll do any harm. Will it do any good?
Do I shop at Wal-Mart? No. So asking me to boycott Wal-Mart is barely symbolic and I bet Wal-Mart knows that. Does Harvard Libraries buy from HarperCollins? I have my suspicions, and asking Harvard Libraries to apply pressure to HarperCollins strikes me as missing the point.