This last time I went a full 3 weeks without needing a manual reset. Unfortunately the server no longer responds to the 'automatic hardware reset' so I've had to request them manually. Now I am going to have them run full hardware diagnostics in the hopes that they find something. My hopes are not high though as I know others have done this in the past without result.
6 weeks uptime with proxmox 2.3 and Hetzner EX6 (Intel Xeon) Here. Looks that there is some kind of incompatibility with some Hetzner EX4/S machines and proxmox like puma said :S
but EX6 (69€) is 20€ expensiver than EX4(49€), and have to pay the setup fee U_U