rocknbil - 6:08 pm on Mar 27, 2010 (gmt 0)

Presumably should I be doing better SEO to retain unique visitors?

"Better SEO" (and marketing, as mentioned) brings more visitors, new and returning.

Compelling content retains visitors, and can increase the average time on site - although compelling content will also bring more traffic as more relevance for particular terms is added over time. It's an exercise in futility if you get tons of traffic and the bounce rate is 99.99% with an average time on site of 3 seconds. :-)

4000 uniques is not all that bad, I have clients that are in competitive markets and are lucky to see 500 - 1000, but most of them aren't doing the work (adding content.)

The nut you might want to crack is why you only have 28 subscribers at 4000 uniques, maybe add something that motivates them to participate in subscription which will likely increase the return visitors.