Nice man! One feature you could add is a GMT time offset? i.e. timezone=10
I will be looking into that, thanks for the suggestion.
Just one thing, can you make it so graphs continue using the last value on missing or zero data? The gaps are distracting 
The upper graph does this already since these values are very unlikely to have huge changes during an intermittent outage.The 'change in wealth' and 'hashrate' graphs do not, mainly because this would be lying and also would not give nice results when prediction is turned on.
The gaps also lets us know that stats were not properly collected for that period of time, whatever the cause may be (could be my server crashed for 4 hours, better show a gap than a lie about it and claim everything went smooth (too smooth in fact).
I appreciate your suggestion though, it just so happens I have already considered this myself
I love RRDTool
Me to, it is often the right tool for the job. Although I really wish it was extent-based.