This is a great question. I spend a good amount of time learning and trying to keep up to date with all the new .NET but it seems that new versions and CTPs are continually coming out across the board.
You'll need to invest a lot of time if you want to keep up with everything, but it's far from impossible - just a lot of time. If your work allows you to try new technologies then you can learn a lot on those projects. If not then you'll want to try technologies on your projects in your own time.
I don't personally keep up to date with everything; I have higher priorities in my life. My general approach:
- Thorough / detailed knowledge of frequently used technologies & future tech directly relevent - Entity Framework, WPF, WCF etc
- Basic / expanding understanding of technologies applicable to my interest or employment - for me this is Enterprise Library (e.g. Unity), MVC
- Overall of all the main technologies - their intent, application, & requirements
I find that I learn enough in the first category at work - learning from co-workers, google et al, or simply putting the pieces together. There's some personal study required but it generally accumulates all by itself. The amount of work involved here is most of my time at my job, reinforcing my skill-set, along with the occasional work at home to brush up on something I haven't done for a while. Just a couple of hours every few months (outside work).
The second category requires much more work. I'm not immediately familiar with the content so I need to study and practice. I don't frequently use these technologies (not at work, & not on a daily basis), so I don't have the in-depth knowledge of, say, all the overloads that I do with my frequent used frameworks. These are the techs that I consider I might use at work one day, so I want to have some experience with them for when that day arrives. The work required here depends on how much tech you put into this category, and how quick you can work/learn/study - anywhere from a few hours a months up to a few hours a night.
The third category is almost non-technical - no code, no implementation. I'll read an article, press release or review but I don't want to read a tutorial or guide. As long as I understand what the purpose of the tech is, how it (basically) works, and the pros and cons then I'm satisfied with this group. It just means that if someone talks about it to me then I can keep up with the conversation, and if I'm eventually exposed to it I'll have some concept of how it fits in. The amount of effort required here is minimal - read an article or release every few weeks.