Well, my view is this on both of them: I'll buy fansubs or download scanslations of a series
that is not available yet in the US. When it does become available, I'll buy the real thing. For instance, I have some Zelda Doujinshi* that is absolutely gorgeous, but it's never been officially translated (and never will be) into English. In this case, I downloaded the scanslations.
But if the series is available to buy, I don't like the idea of downloading scans of it. Maybe you want to find out what the series is like before buying it ... um, I'd check the library first, or read half of it in the bookstore (I'm convinced that Borders put the chair in the manga section just for me
) before using a scanslation site.
If unreleased scanslations gets you hooked on a good series, that's great. But I hope it get's you hooked enough to buy the real deal when it becomes available.
*
Doujinshi is almost always associated with hentai. Just clearing up that "doujinshi" means a manga written, drawn, and published by fans. I do not have hentai Zelda scanslations, I have a perfectly clean Zelda manga made by fans. It's really good too! Here's a sample of the art: