I haven't been to any, but from the google group it looks like London also has quality meetups pretty regularly.
This is my favorite getting started on d3 tutorial: http://www.jeromecukier.net/blog/2013/03/05/d3-tutorial-at-s...
This is my favorite getting started on d3 tutorial: http://www.jeromecukier.net/blog/2013/03/05/d3-tutorial-at-s...
If someone considers writing a d3.js tutorial, I'd urge them to use a real example, since this is where people realize they should use features like line.defined(), figure out how to implement gridlines yourself, and so on.
As great as d3.js, it's really hard to dive into the official wiki/docs as well as hit them for help.
I've made lots of stuff with d3 and never needed grid lines or dealt with undefined line values, so my 'getting your hands dirty' tutorial would probably deal with totally different issues than what would be useful for you. At a certain point, you just have to buckle down and read the documentation - a quick peak at the page for svg.axis shows how to get grid lines extremely easily (http://bl.ocks.org/mbostock/4323929).
Hanging out on the stackoverflow tag is also super helpful. I either know how to answer a question and get some internet points or Lars responds within an hour and I learn something new.