The main R Project website, www.r-project.org, many of the primary CRAN mirrors (including cran.r-project.org), and r-forge.r-project.org are currently unavailable following a power failure at the master host in Austria. The US CRAN mirror, cran.us.r-project.org, and other mirrors not under the r-project.org domain (including cran.revolution-computing.com) are still accessible. In addition, the following services are not affected: bugs.r-project.org, developer.r-project.org, ess.r-project.org, search.r-project.org, svn.r-project.org, wiki.r-project.org, win-builder.r-project.org.
Downtime of at least 24 hours is expected.
Update Apr 27 09:34: The R Project websites appear to be back online.