I'm currently doing a distance learnig course, leading to the RHS General Certificate in Horticulture. A completely pointless exercise (much like this blog!), but nevertheless enjoyable.
I get a sense of satisfaction from learning, and learning combined with my hobby is better still.
The General Certificate is suitable for all, including hobby gardeners wishing to learn a little more about the whys and wherefores of plant growth and cultivation.
It's something to do in the dark winter evenings, which are quickly coming upon us...