Some of the buttons and switches, such as the AF-ON and the AF-Area mode selector, have a more distinctive, easy-to-feel design than their counterparts on the D200. The overall configuration of the controls works very well, but I do have some personal nitpicks. For example, I really like the switch for the AF-Area modes, and would have liked a similar feeling control for the metering selector, to allow for thumb-only operation, as like the one on the D3.
If you're familiar with the AF modes of the D200, you'll notice that the D300 lacks the Group Dynamic AF mode of its predecessor, which allowed you to clump tracking AF points. It seems to have been replaced by the ability to choose from 9-, 21- and 51-point AF options, which essentially serve as different tracking AF-point clump sizes. The 3D tracking is only available with the 51-point AF mode, however.
Nikon swapped the bracket control on the D200 for the review button on the D300. To select bracketing on the D300 you use the one of the programmable buttons (default is Fn, and the DOF preview and AE-L/AF-L are assignable, as well). Frequent bracketers might miss the dedicated control, though.
On the upside, the D300 sports a big, bright 3-inch LCD. Increasing the display size hasn't adversely affected the ergonomics of the camera at all.
Very little has changed in the physical design of the D300 over the D200, but the few updates are definitely for the better. For instance, Nikon has moved the flash sync terminal to the front with the remote terminal, and substituted the easily lost nontethered, nondustproof covers with tethered rubber plugs. The focus-mode selector-switch mechanism remains the same.
The ports on the side, which now include an HDMI output in addition to composite, USB, and DC-in ports, share a single rubber cover, as opposed to the separate USB section on the D200 (not shown).
The release mode dial provides access to the various shooting modes--single, low-, or high-speed continuous, Live View, self timer, and mirror lock-up.
If you plan to use the D300 as a supplement for the D3, you may get frustrated by the control layout differences between the two. For example, on the D3, the quality, white balance, and ISO buttons reside on the back below the tertiary LCD, rather than above the release mode dial, their location on the D300.