Installing Datamapper on Ubuntu 9.04, I got this mysterious error:
$ sudo gem install do_mysql
Building native extensions.  This could take a while…
ERROR:  Error installing do_mysql:
ERROR: Failed to build gem native extension.
/usr/bin/ruby1.8 extconf.rb install do_mysql
extconf.rb:3:in `require’: no such file to load — mkmf (LoadError)
from extconf.rb:3

After much googling and trying other solutions like installing libmysqlclient16-dev, I stumbled upon [...]

Rails stopped routing http requests the morning after everything was working fine. I was running demo exercises from the Agile Rails book and didn’t seem to do anything that could have messed up the installation. Downloading and symlinking to the books own app code didn’t fix the problem.
“no route found to match [...]

I’ve been seeing an unusual number of spam comments awaiting moderation lately.  Normally, Akismet does a great job keeping them out of the moderation queue.  The ones that do make it to the queue, I usually let expire automatically.  This new crop, I decided to delete manually.  When I did, I got this error:
Unknown column ‘pingback_views’ in [...]