Even paying apps go for for a sale, less often though. For me Pocket is so seamlessly integrated with my online presence that it will of course to see it go(considering acquisition will kill it or somehow make it unusable - ad etc) but the ease/swiftness makes to very hard to switch to any other service paying or non-paying.

One example is their Android focus which, sometimes I funnily think, developers like Marco despise(no, read ignore :P ).