Several stories in recent mainstream magazines indicate that in the current economic climate an increasing number of people are being more self-dependent: doing their own home repairs, making their own clothes, fixing their cars themselves rather than taking them to a dealership. Certainly the motorcycle industry is in the same shape. New-bike sales are down, but my sources indicate that sales of aftermarket and OEM parts are doing well as motorcycle owners are increasingly looking after their own bikes. I think that's a good thing.
Another facet of working on your bike is that for a lot of people it's therapeutic. I spent a lot of late nights in the garage when I was racing, and most of the time that was just as enjoyable as riding. Fixing something like a broken crankshaft with only a few hours to do it, now that's a different story... Some riders I know enjoy having an icy beverage or two while working on their bikes, and sharing the experience with friends. Others like the solitude of working alone and find that more enjoyable. Either way, the satisfaction of a job well done is the same (unless a few too many of those beverages were involved) when the maiden voyage occurs.
For a long time I've thought that the more familiar you are with the inner workings of your bike, the better a rider you will be. And the one sure way to know your bike inside and out is to do your own maintenance, repairs and upgrades. Riding skill and mechanical (and, increasingly in our sport, electrical) knowledge may not seem to be logically intertwined, but I've seen plenty of examples that show otherwise.
If you've never undertaken your own maintenance or upgrades, you may be surprised at how simple most things are. A service manual is mandatory in this age of multi-piece bodywork and miles of emissions plumbing, but most tasks are straightforward when broken down into the necessary steps. The proper tools definitely help, as does patience and a notebook to help remind you where everything goes. Start with the simpler things that don't require special tools-like an oil change or adding a slip-on-and gradually progress to the more complicated service items and add-ons. Most of all, be patient and enjoy the experience. And then enjoy being a better rider for the experience.
Consider, for a relatively simple example that can quickly get complicated, your bike's throttle. In its simplest operation, the more the twistgrip is turned, the faster your bike goes. This is the relationship a new rider deals with. At a deeper level, however, there is much more involved. A larger-diameter throttle tube can change how quickly the butterflies open when the twistgrip is turned. An eccentric throttle tube more subtly changes the relationship, opening the butterflies relatively less at smaller throttle openings, more at full throttle. How can this help you as a rider? Say you're struggling with abrupt throttle response from your bike. Knowing the options available will allow you to fix that problem and go on to concentrate more on other aspects of your riding rather than constantly dealing with that one problem. And if you perform the upgrade yourself, you'll be more aware of what exactly the changes are as opposed to taking someone else's word for it.
We can go even deeper into the same example. At the other end of the throttle cables, your bike may have secondary throttle plates or electronically controlled butterflies. Electronic trickery lets you change how the butterflies behave in relationship to the throttle even more subtly than simply changing the tube. The more familiar you are with your bike's internals, the more aware you'll be of just what you can alter to help you.
The same applies to almost any aspect of your motorcycle. Actually filling a fork tube with oil and seeing the air gap left over will help you better understand how that affects your suspension under braking. Swapping sprockets and counting teeth will give you a better appreciation of how a gearing change affects acceleration. And changing tires and feeling how one is much softer than the other will help you to take advantage of each tire's characteristics.
As an aside, the concept of knowing your bike inside and out can be taken a step further. Researching some aerodynamics helped me tuck in better at Daytona when I raced there, and I always posted good trap speeds (the engine my brother built didn't hurt either). You can learn a lot about rake, trail and geometry and how they interact by picking up some basic trigonometry knowledge. Or you could research basic mechanical design to better understand how suspension linkages and springs work. The more information you have in your mind, the better equipped you are to take full advantage of the bike you have, solve problems, and make modifications.