My experience is if they don't come up with your cd(s) within two weeks, they cancel the order. The last time I took advantage of there sale, I received 2 of the 4 discs. Two were placed on backorder. A good time had passed and I wondered of there status. I called there 800 number and that was there response. I wish I knew of this beforehand, since I saw one of the recordings in a store and passed up on purchasing them.
My experience with J&R on backorders is pretty dismal. If the item doesn't clearly show "In Stock" on their site, I don't even bother to put it in the shopping cart.
I found that the not-in-stock, "ships in 2-4 weeks" (or whatever) items basically never shipped, and just slowed the rest of the order down by two weeks.
[Added] Just got e-mail from J&R pimping a "Jazz Sale". In addition to the BNs, there are a lot of OJCs for $7.99. Their best sale prices on OJC have been $6.99, but the $7.99 level may still warrant adding a few items to BN orders...