Don't get me wrong - We've done both!
Creating satellite assets proved to me a nightmare for us on so many levels it's not funny. From using up resources, splitting up time for creating links across multiple sites to client complaining about the look and feel of all these microsites (they treat them as any other site). I've abandoned the method soon after that and put our resources in link, bait, content and whitehat link building. It gave us the results we needed.
To be fair I recognise some promotional items operators in Australia who have done microsites really well and benefit from it, however most of them have "fed" juice through the main corporate site. To me this is too close to a scheme for comfort.
Another point (this time against the method) is that you're missing out on branding and effectively creating natural links to microsites. If we look at all big brands, their microsites are campaign based. not designed to attract SEO traffic, that's the job of the main site.