So first thing I do is go create a graph of page views and twitter mentions, this seems like a great thing to see how these are linked. The problem is that mentions is so much lower than pageviews it creates a meaningless graph. Also, when I edit a graph it creates duplicates on the trends.
Allowing you to view data with different scales is something we are looking to support very soon. We actually support that automatically for different data types (like viewing currency and numerical data on the same graph), but we are working on the best way to support that for same type data.
One thing that may help a bit in the meantime is that you can zoom in on your data sets by click and dragging on a graph.
As for the duplicates you are seeing, can you tell me what steps you are taking to get those? And what browser you are using?