Are handlebar risers really necessary? Well, one of the most important things when riding a bike is maintaining the correct posture. I found that with the stock handlebars, I tended to adopt a slightly crouched position. In order to sit upright, the handlebars needed to be moved slightly upwards and towards me.
I looked at installing some "Helibars" but the price was ridiculously high (I see that they've stopped listing helibars for the ST1100 now anyway). Instead, I chose the Genmar spacer design from the very helpful people at Motorcycle Road and Race
These raise the bars but retain the stock angle, which is important in maintaining an even weight distribution across your hands during braking and turning. I see they now do several different heights; the original 20mm height was fine for my purposes.
Unfortunately the installation of these necessitated the slight butchery of the handlebar cover:
Using a piece of scrap metal, I made up a small bracket to hold the front edge of the handlebar cover securely in place, as the original bracket was now too short to be of use. You can just see part of the bracket in the photo (above the ignition switch).
Also, I found it was now a bit fiddly to turn the ignition key, so I bent another piece of scrap metal in half and with my mig welder, attached it to the key, giving it a slightly longer reach.
Conclusion: If you're tall, handlebar risers make for a much more comfortable ride!