A certain percentage of your time as an employee must be allocated to maintaining your professional status. For example reading industry/technical magazines, dead tree or on line versions, attending courses and seminars, etc.
I figure about 10% of your time should be spent that way.
(Staying away from hard numerical suggestions) I'd say that percentage needs to rise as you spend more time in the industry. The natural progression I notice is:
1) Courses/seminars: 3-5 years behind (OK, be fair, sometimes 10 ;).
2) Books: 2-3 years behind.
3) Tech magazines: 1-2 years behind.
4) Real conversations (with Graham's "great hackers"): 6 months behind.
5) Build it yourself. :)
But each move closer to "now" means less distillation by those before you, and more personal time required to filter/integrate the info.
I've only been doing IT (professionally) for six years; I can't remember the last time I read a tech magazine article whose content wasn't 'obvious' (due to personal constant exposure). I haven't bought tech books in over a year (OK, you got me, I just bought Fowler's _Patterns of Enterprise Application Architecture_, but there wasn't anything new in it (which he warned me about in the foreword, but I bought it anyway)). Seminars were never interesting.
I'm done rambling, so I'm just going to peter out there without a conclusion. :)