IMHO the popularity of R is grounded on its compatibility with S/S-Plus. if they hadn't used S as language, they would have never reached the position where they are now and R wouldn't be increasingly adapted as standard statistics package---competing with and/or replacing SPSS/PASW, SAS, stata etc.

On the incanter homepage there is a link to http://www.jstatsoft.org/v13 which includes a few interesting articles.

Anyway, I find the integration with java interesting. That's a strong argument in favour of a solution like incanter.