I've just seen nowadays they guarantee 99% Network availability.
None of my 7 servers has ever suffered a hard disk crash or similar, which is nice but not actually a meaningful data point. (Another nice point, internal traffic is free, even between their data centers)
Their support is top notch in my experience, answers within 15 minutes with the free support. Just read a random post in their support forum, they switched a defective power supply within 2 hours. They once phoned me because one of my servers was behaving suspiciously.
All in all, if you can live with 99% uptime I don't know any provider that's cheaper or has better support. (They do have failover IPs (http://www.hetzner.de/en/hosting/produkte_rootserver/flexipa...) and high availablity packs (http://www.hetzner.de/en/hosting/produkte_rootserver/option-...) but that doesn't help with the 99% network availability)