How are you storing them, and what do you use to read/visualize/analyze them? I'd imagine just putting them up in a UI becomes a needle-in-a-haystack issue. Are you programmatically analyzing them?

Honeycomb. For shorter traces (most of them), a waterfall view is great. For those long ones, we try to split them up if it makes sense but you can also just run queries scoped to that trace to answer questions about it (how many of the spans are db queries, how many are this query, are they quick, etc etc)