Supplemental results and sandboxing

any relation?

[bcc1234]

I have a new (four-month old) site that has 15 pages in the main index and around 1400 in the supplemental index. All unique content (not scraped, not re-written articles, etc).

Right now, I'm getting maybe 10 referrals per day from Google.
It feels like there should be more traffic for the long-tail keywords.

The home page shows a toolbar PR 4 for what it's worth. Some internal pages show 3. Google webmaster tools shows an average of 120 pages fetched per day by the Googlebot.
So everything looks normal, except for the referrals.

I'm not after a few competitive keywords, so I'm not really worried about the sandbox effect.

I'm wondering if the fact that the site doesn't appear in the serps for some really unique phrases is due to the sandbox effect which would fix itself eventually or if it's because the site is in the supplemental index?

Or is there a relationship/dependency between the two?

[tedster]

Matt Cutts recently explained that URLs in the supplemental index are not indexed as completely as URLs in the main index. That is, they tend to be "tagged" only for a few key words, not for their entire content. I think this may be the reason for your lack of long-tail search traffic.

Some modest further growth in backlinks may be all these PR 3 URLs need to move into the main index. In the meantime, I suggest that you ensure they all have uniquje and page-specific titles and meta descriptions (that plays into the incomplete indexing.)