Today's HDSLRs are clearly very capable still cameras. If you look at them from a perspective of a professional filmmakers there is a lot missing.

These cameras would not even be looked at by film makers if they would not deliver stunning images due to their relative large sensors. Unfortunately not all the time

Lets look at the positive and also negative aspects from the perspective of a filmmaker.

Pro

• Top image quality at times (see the Cons for issues like aliasing and moire)
• Amazing low light capabilities (Canon 5D Mark II, 1D Mark IV and Nikon D3s)
• Compact
• Relatively cheap in the movie world (often used as second unit cameras and/or for special tasks)
• Can produce shallow DOF with a very filmic look
• Good prime lenses much cheaper than film lenses

Cons

• Aliasing and moire can be a show stopper (especially at 720p). This is the #1 concern I hear from professional videographers. Shooting people is fine but detailed structures (combined with movement) easily shows both moire and aliasing
• Swivel LCD needed (here the Panasonic GH1 shines)
• Full HD output for a second monitor (some Canon cameras can be partially used for this but the camera LCD shuts down)
• Way better solution for sound needed
• Cameras can have noisy operations (e.g. IS). Here the GH1 is again showing the way.
• Codecs limit the final quality (higher bit rates needed or even some sort of RAW output like the RED One).
• Built-in ND filters needed
• Better help with exposure and sharpness (zebra stripes and focus aids). The GH1 supports at least a live histogram.
• Help with follow focus (wireless and controlled by the camera)
• Most DSLRs don't have a swivel LCD (The GH1 being a positive exception)

Conclusion

This is just the beginning of this interesting convergence. We are not complaining here but believe that the manufacturers can do better and we have to push them. We find that these are exciting times and we are part of it. If you look at sample movies on the net (Vimeo and YouTube) then you can see what excellent work is produced today even considered all these limitations. Like in still photography the results depend so much on the artist and it is not a good idea always to blame our cameras.