Seldom do I need two parts to an article topic but this is one that demands it. So you find it laborious to switch between the realm of autofocus and manual? It does take time and its something we may not have when we want to capture that precious second.
Here's how to combine both manual and autofocus feature of our Nikon D90 without needing to flick the AF/M switch ever again! But note this only applies to the Nikon D90 kit lens and perhaps the newer lens lineup. (Will not work on the 50mm F/1.8D)
Go to Menu F4 to switch the AE-L/AF-L assignment button to AF-ON. Switch your AF mode to AF-C. Done. Now, if you want manual focus override, simply turn the focus ring (on the kit lens) to obtain focus and depress the shutter release. If you fancy autofocus suddenly, depress the AE-L/AF-L button to get auto focus. Depress shutter release to shoot.
Now, in your hands, lie the power to shoot automatically and manual in a split second response time with the Nikon D90!