We know that google isn't perfect in this sense, but you can add the "forum" word to your search query. This will certainly make the forum appear at the top. We use google search because soon Nabble will have several different servers (n3, n4, etc.) and google can easily integrate this distributed search.
We will use google search only to find pages globally (across all Nabble servers). Internal forum search won't change and will continue to be the same (mainly because google can't search private forums and messages). So this will remain intact, don't worry.
Part of what I love about Nabble search results is probably thanks to Lucene. The other part that I love — the clean, simple, minimalist, restrained appearance — is surely thanks to Nabble. The appearance lends itself extremely well to speed-reading and the minimalism is never a barrier to finding something quickly.
I recall reading somewhere that a magic number '3' applies to people's perceptions of Google search results. Something like: if the result is not in the top (uppermost) three, then that result may be overlooked or ignored.
What's interesting here in Nabble is that a higher magic number '10' (results per page) seems to work very well. All ten are easily scanned and when searching becomes complex, I never feel that I'm wasting my time. The absence of images certainly helps.
(In another environment (Diigo) I'm pleading for appropriate use of well-sized thumbnail images (echoing what I like about Glims thumbnail enhancements to Safari, and uses of thumbnails in many other environments), but the Diigo use case is very different; most content there is abstracted from web pages that have a 'look and feel'.)