If you look on Cultured Code's Arrivals page, you'll see something like this:
This is a very tempting thing for small companies to do. You want your customers to know that you're working on something they want.
But ultimately, it's a bad idea. When Cloud Sync launches, I'll think, "Finally." If I didn't know they were working on it, I'd think, "Oh, Cloud Sync! Finally! Sweet!"
That is, when it's released my thoughts will focus on how long it's been on their Arrivals board. I won't think about all the awesome stuff they released in the meantime, some of which may have been more valuable than Cloud Sync.
Under promise, over deliver.