Hi. As I wrote in my recent post I'm a professional video editor who know very well AVID, FCP and Premiere.
I'm very interested in opensource world so I decided to give my contribution to the Kdenlive project which seems can to reach soon professional standards.
So I used Kdenlive for some weeks and I made a list of missing features that professionals always use and how to work around before these are implemented.
I hope you'll appreciate these suggestions and I remember you I'm italian so I hope you can understand my english.

1. Audio mixer panel: as I already wrote this is a very usefull tool for have a volume control for whole tracks, for using effects on the track and not on the single clip and for using bus features. Anyway the mixing way on the timeline even if very slower to use and less productive it already works well.

2. Trinmming window and advanced trimming features. Generally professionals use 4 ways for trimming, rolling, ripple, slip and slide.
rolling: http://helpx.adobe.com/premiere-pro/using/trimming-clips1/_jcr_content/main-pars/image_1.img.png/es_16.png
ripple: http://helpx.adobe.com/premiere-pro/using/trimming-clips1/_jcr_content/main-pars/procesure_18/proc_par/step_1/step_par/image_0.img.png/es_19.png
Slip: http://www.3dmax-tutorials.com/Adobe_Premiere/images/es_05.gif http://helpx.adobe.com/premiere-pro/using/trimming-clips1/_jcr_content/main-pars/image_2.img.png/es_20.png
SLide: http://www.3dmax-tutorials.com/Adobe_Premiere/images/es_07.gif
With the basic trimming functions Kdenlive has now, you can do nearly all these features by using more passages. The only thing you can't do at this time is the slip feature. This last feature is very usefull during the 3 points editing.

3. Match frame. This feature opens in the clip window a clip at the frame you're watching in the timeline. My work around is: use the split feature, open the clip properties from the timeline, copy the timecode for the in point, undo the split command, open the clip from the project and copy the timecode in the clip monitor.

4. Nested timelines. In some old version of Kdenlive this feature was already present. Now you can import a project as clip in another project but you can't have different versions as timelines in the same project. Then, if you have to change something in an imported timeline you have to close the project you are working on and open the one you want to edit.

5. Preview rendering. The idea to use proxy feature is good, anyway the render preview feature in the timeline, as all major softwares have, is fondamental. If you need to check a very complex effect you can't watch at it in compressed way, you need the whole quality and smoothness of the final rendering without the needs of exporting it. You can't even make chroma key or color correction by using compressed clips. When you switch from the compressed to the uncompressed clips the result can change drastically.

6. Extract and lift features.

7. Mulitrack editing. With the split view now already available you can reach the result but not in a productive way.

8. Photoshop psd or Gimp xcf layers importing. This is usefull for layers animation. Now you must create a separate file for each layer.

9. Bars and tone generator. http://www.youtube.com/watch?v=zoNMlpMaUYk
As work around I use a tiff image in 4:3 and one in 16:9 and a 1000hz wav clip.

10. Safe area marker. http://forum.videohelp.com/images/guides/p1716418/safe.jpg
As work around I created one 16:9 and one 4:3 trasparent png which I put in the video1 track

11. Advanced tools as shadows, kerning, etc in titler.

12. Show the complete waveform in clip window when open an audio clip, not only frame by frame view.