I’ve just published version 2.5b15 of the post plugins: Similar Posts, Recent Posts, Random Posts, and Recent Comments. Thank you to all who have found bugs and especially for those who have tested and re-tested when I couldn’t reproduce the bug myself.
There have been particular problems with the installation of Similar Posts on some systems and with the behaviour of Random Posts as a widget (seems to be a language issue). If anyone has difficulties with these or any other bugs please contact me. The best way is via the Bug Report screen in the plugins’ options/settings pages but a comment or email will do if you remember to give me enough information about your setup to help me debug.