The best way to keep your devs up to date with the latest and greatest is to actually implement it in your products. In my experience it is great to learn about new stuff, but the effect of the learning is limited if you are not actually putting it into practice. Not to mention that you are also limited by the teaching/presenting capability of the person doing the teaching, and the aptitude of the people doing the learning.
I've worked in a company that promoted a once-a-week learning session, and it was largely ineffectual. The idea is great, but putting it into practice is harder than it might seem. I resented taking an hour out of my already very busy schedule to be at these sessions, and i hated it when it was my turn to present because it can take a few hours to put together a decent presentation.
You also have to bear in mind that different devs have different aptitudes. Some learn very easily and will love finding out about new technologies, they will have 300 different feeds loaded up in their blog reader. Some will be quite content to stick with the stuff they learnt in the 80's, they don't care about F# and MVC and MVVM and IoC and WCF and REST.
One way that may be productive for you is to have your most senior/knowledgeable devs do regular code reviews with the other devs. Keep the reviews short, non-competitive and informative, that way tips and techniques can be passed on in a one-on-one situation, and as the "learning" will be in the context of some actual work the devs will remember it a lot easier. The key to this is keeping it fun, and being able to relate the concepts/techniques to something real.
Another thing to try is to have 6 monthly reviews, and set some objectives during those reviews. An objective can be to learn something about XAML and WPF, or to write a simple Hello World that retrieves text from a WCF service, or to study for and pass an exam. Make sure the company is in a position to assist them with this by buying books or paying for exams, etc., and you will very quickly be able to single out those who want to learn and those that are just content to get by with what they already know.