Regarding the memory hog it is, I wasn't really able to see that its benefit can outweigh this. The previews are not very good formatted, thus not very informative. Also, when pinning the interclue window, it doesn't stay pinned when navigating to the next page of search results, e.g. on Google. So you have to pin it again and again. Before installing Interclue, FF took about 100 MB with all my addons. After installing this addon, FF suddenly took up more than 200 MB of memory, just hovering around a bit on 2-3 websites. After uninstalling Interclue again, FF went back to 100 MB. However, apart from those issues, I guess Interclue is a nice idea.
There are options which help improve the memory issue, and we'd also like to know what firefox version and operating system you were using - please contact us at http://interclue.com/contact.html - Leaving the 'pin' turned on or off on a per-domain basis sounds like a reasonable idea, we'll give it a try as soon as we can. There are some problems when it gets pinned and then you resize the browser that will take a little working out, but we'll get there.