I recently purchased a new Nikon D300s, and I am not satisfied with it. In fact, I'm disgusted with it! I paid $1800 for this camera, and it can't do any of these basic functions, most of which are just software/firmware things that could be added without any hardware tweaking. Although this list specifically applies to the D300s (because I own it and know what it can/cannot do), a lot of the things can also apply to lots of other digital SLR cameras that are produced by Canon, Sony, Fuji.... (specifically the ones with a video mode):

1. There is no sound detection shutter triggering.
2. There is no motion detection shutter triggering.
3. There is no headphone output.
4. There is no sound metering/VU/Volume/Peak meter in camera.
5. You can't record audio files.
6. The only image recording options available are JPG, TIFF, or NEF. The only video formats available are .AVI.
7. Nikon has limited the frames per second. The camera is capable taking 8fps without an external battery pack, but in order to enable 8fps properly, the camera has to detect that there is a battery grip attached. The only reason why they did this was to make you buy their $200 MD-D10 battery grip.
8. You can't write your own programs for the camera because the firmware is not open source. The majority of these problems would be solvable if it was.
9. You cannot view non-Nikon content in camera on the LCD screen. All images and videos must be taken by a Nikon camera in order to be played back in camera.
10. It can't meter beyond 30 seconds.
11. It can't blend multiple exposures in certain, useful ways.
12. It only can do whole number fps integers (4fps, 5fps, etc) and is unable to use more flexible values, such as 4.2 fps or4.3fps, for example.
13. It can't do 2 fps and then 3 fps, and then loop that pattern.
14. You cannot bracket images with user customized integers/values.
15. The exposure bracketing only allows up to a maximum of 9 stops.
16. The self-timer only has 2, 5, 10, or 20 seconds available for customization. What if I wanted 8.5 seconds? What if I wanted 40 seconds, or 8.2 hours?
17. The exposure delay mode can only be set to 1 second.
18. You cannot properly set the white balance in camera for infrared photography. This feature was available in some older models.
19. The file naming system is very limited. It allows only three characters, an underscore, and then the numbers 0001-9999. What if I wanted the file name to have an unlimited amount of characters at the beginning, and then the file number (say 12095356342 (as you can see, it can go past 9999 without being reset to 0001 or no reason)) and then another set of characters, and then the date (a custom variable)? Nope, sorry.
20. The Active folder function is limited. Yet again, it only allows three numbers to be inserted into the folder name, and then a "D300S" is stuck at the end of the folder name. What if I wanted an unlimited amount of customizable numbers AND letters?
21. There is no live histogram.
22. The live horizon only meters the x axis, not the y axis.
23. The BULB mode is limited. It lets the photographer take an exposure while their finger is pressed on the shutter, but if they wanted to push the shutter once to activate the exposure, and then once again to stop the exposure, they wouldn't be able to do that without buying a cable release or remote.
24. EV, Exp, and ISO is adjustable only in 1/3 or 1/2 increments.
25. Accurate exposure times are limited. For example, you cannot set it to 23 seconds. It's either 20 or 25.
26. It only can write files to be in horizontal orientation. It can write in the EXIF data that it needs rotating, but if you wanted to write the actual file dimensions in vertical orientation, its is impossible.
27. It's incapable of auto-focus bracketing.
28. The AF Assist lamp doesn't always turn on when it's dark, and furthermore, there is no option to turn on the AF Assist lamp at your desire. It is a waste considering how bright and useful the lamp is.
29. The Interval Time Shooting mode is limited. The shortest interval time is one second.
30. There is no way to tell how large the file size is for any of the pictures in camera.
31. There is no option to view the pictures in whatever orientation your camera is in. It's either "ROTATE TALL" or a not.
32. You cannot install different sized crystals inside of the camera body that are in front of the sensor to bend light in certain artistic ways (this one is a joke)
33. You cannot auto-focus the lens from Focus Point A to Focus Point B while it is taking an exposure.
34. The exposure compensation only goes up or down to maximum of five stops.
35. You cannot easily select groups of images to be deleted simultaneously.
36. You cannot quickly create a playlist of certain images/videos you want to play while in sideshow mode.
37. You cannot resize images to smaller sizes. This feature was available in older models.
38. The repeating flash mode is limited to 1HZ to 50HZ. It's very easily possible to program the camera to be .5HZ.
39. There is an option that allows you to trim movie clips from the beginning, and another option to trim movie clips from the end, however if you wanted to do both at the same time, there is no option available. You have to trim the beginning, which makes a new copy of the file, then trim the end of that copy, which makes another copy. In the end you have 3 copies.
40. You cannot create a movie file of a long exposure being recorded in real time.
41. You cannot set the shutter speed for movies.
42. There is a hissing sound when using an external microphone. Why can't they just make the thing work normally? normal = functional.