I would argue that I'm current on the machine learning and practical software development side and minimally current on the others and improving.

To offer some background, on the machine learning side I've built and deployed over one hundred models using nearly every major machine learning technique available today. To stay sharp I actively compete in Kaggle and other competitions (and have won a few small competitions) and have attended over six large ML conferences over the past two years. I actively read through every major published book on machine learning and nearly an entire bookshelf dedicated to the practice. These books, as well as MOOCs contribute to the majority of my reinvestment time on this side. I turn around and directly apply this information to competitions and paid projects to help it stick. I also read through as many ML papers as I can budget time for. Arxiv Sanity Preserver is a great resource here (http://www.arxiv-sanity.com/).

On the software development side I've built and deployed over a hundred websites products and services in half a dozen languages over the last twenty years for clients or my own business. I subscribe to a litany of aggregators over python, c#, and javascript news and use that information to identify trends to focus on for the practical side. Outside of side projects to gain practice these skills I also use pluralsight, developer conferences, and (less frequently now) books to stay current on this side - which contribute to time against this daily.

On the computer science side I have a large collection of classic books I'm working through and rereading. Everything from the Intro to Algorithms to SICP. I'm currently on my second pass through MIT's 6.006 and 6.851. Much love for Erik Demaine. I own a collection of CS puzzle books including Cracking the Coding Interview and my wife tortures me weekly with dynamic programming puzzles on a whiteboard we have to keep sharp. Similarly, I also tackle LC and HR puzzles on a weekly basis.

On the marketing side I've managed a significant of marketing spend for clients and my own projects through every major marketing platform except facebook. Through this I've developed a skillset around split and multivariate testing. I've also run literally hundreds of marketing experiments to gain experience and understanding. I actively manage paid and organic marketing efforts for an array of projects which provides an additional impetus to stay current. To that end, I subscribe to a number of marketing news aggregators and I'm reading through every major marketing classic I can find. I've had more trouble finding good information on this side compared to other areas.

On the design side I'm currently taking courses through Kadenze and own every a large collection of design classics that I've been reading through. Everything from universal principles of design (strongly recommend) to the design of everyday things. Beyond thoughtful practical application of these skills in hundreds of websites and apps I've also exhibited artwork.

It's a similar story for the remaining areas. Mostly paid courses, conferences, and classic textbooks (I budget about 20k a year for these resources). I also use Anki for remembering important concepts.

I've been at this (reinvesting continuously in all of these areas) for over ten years and averaging 15-20 hours per week of dedicated reinvestment with nearly no breaks for at least the past three years.