How Big Is Your Store?

I’ve just kicked off a project to explore changing our main content repository to an RDF triple store. The main issue at the top of my list is scalability.
The repository will end up holding metadata about more than 16 million articles (plus their associated authors, affiliations, publications, etc) and as you’d imagine thats going to end up exploding into a large number of triples.
Reading through the Semantic Web Storage and Retrieval report I came across the following, which concerns me a bit:

Stores that can handle 10-20M triples are readily available and the current state of the art is around 40M; the development community is considering the next 10x increase in storage requirements, and their affect on indexing, which has tended to be O(n) for triples. Novel dedicated storage approaches such as in RDFStore were shown to avoid this. The dedicated non-relational stores can outperform the relational ones in such scaling, although the relational databases continue to perform well.

Basically I’m wondering whether I’m being a bit ambitious?
I’d be interested to hear about how big a store people have worked with, including which APIs, etc they’ve been using.
To give a bit more context, as we’re mainly a Java shop I’ve begun by considering any store that can be plugged into Jena. So the Jena persistence model support would be my baseline, with Kowari being another candidate. I see that RDFStore may be adding Jena support so we may explore that too.
I have no strong preferences for a relational versus non-relational store, except that there are other benefits (backups, distribution, etc) that I doubt are “baked in” to other custom stores. What am I hoping for (but haven’t ruled out) are creating a custom database for our content, but I wanted to avoid some of that pain by using off-the-shelf toolkits.
Commenting is switched off (spam problems) so if you’re interested in sharing experiences please send me a mail. I’ll write up notes on any responses I get with an aim to sharing them with the rest of the community. I’ll do the same to write-up our prototyping experiences.