After receiving yet another 'please login and click through our captcha for no reason' e-mail from a DynDNS provider, I decided to run my own DynDNS server.
As I already run my own DNS servers, this was just a matter of adding a dynamically updateable zone and writing a script which receives the IP change request via HTTP and sends out a DNS update.
Luckily the DynDNS API is quite well documented and I quickly came up with the PHP code below which performs the task well enough for me. Feel free to use it to run your own DynDNS server.
PS: to any friends reading this and looking for a DynDNS service: drop me a message and I'll set you up with an account.