I stumbled over a bug in hsolinkcontrol, which also seems to be reported in this pharscape forum post Bug description:

• Ubuntu 9.04, with NO(!) resolvconf package installed
• hsolink 1.0.118 package
• HSOconnect 1.2.18 beta
• /etc/resolv.conf is saved to /etc/resolv.conf.hsoc%s.tmp
• the permissions of the created /etc/resolv.conf.hsoc%s.tmp file are 660 and root:root
• when the saved /etc/resolv.conf.hsoc%s.tmp is moved back to /etc/resolv.conf, this file also gets the 660 permissions
• after that, only root can read /etc/resolv.conf
• the effect is, that DNS resolution does not work except when you are root
• installing resolvconf will work around this issue

This can probably be easily fixed, by making sure that the /etc/resolv.conf.hsoc%s.tmp has the same permissions as the original /etc/resolv.conf file. Since installing the resolvconf package makes the bug go away, I did not fix the source, but just sent a notice to the author.