It is true that making /var/cache/pbuilder/build a tmpfs makes a noticeable speed difference. But it seems you cannot cache the downloaded debs: ln: creating hard link ...: Invalid cross-device link.
pbuilder with default settings will fail to build a package depending on sun-java5 or sun-java6, because the license needs to be accepted first.
Now some time ago I saw a patch for pbuilder itself to “fix” this, but for the time beeing I used to set DEBIAN_FRONTEND to readline in my pbuilderrc. But today Michael Koch came up with much better suggestions: Preset the debconf value in the CHROOT and save it.
It’s pretty easy:
$ sudo pbuilder login --save-after-login # echo "sun-java5-jdk shared/accepted-sun-dlj-v1-1 boolean true" | debconf-set-selections # echo "sun-java6-jdk shared/accepted-sun-dlj-v1-1 boolean true" | debconf-set-selections # exit
and voila, problem solved. Thanks to Michael for the tip.
Update
Manual Prinz suggested a slightly different way, that realizes the same debconf setting, but with hooks:
http://lists.debian.org/debian-java/2008/05/msg00024.html.