Where was it?
I could see this being useful in some cases.
Perhaps search could search by id if only a plain number is used?
I could also see it be useful to have an auto linker in posts when text meets a certain pattern like #123 (ignoring the obvious hash tag conflict for the moment)
May be better to think of doing this kind of thing via a plugin or opt-in site setting though.
@ronteras can you tell us a little more about your particular use case?