I been running into a few problems lately. Not with the initial copy of Ubuntu, but those applications I choose to use in it. KDENLive is just one of them. I had been running with problems with the initial dependency of a file which was required by it to get passed the setup wizard screen. I broke this myself by attempting to fix problems I was facing with rendering videos into any mpeg format, which resulted in irrecoverable consequences. 

I've mentioned in the past videos, that majority of what I see problems lye is not from the post install, but those applications & drivers that are not the community maintained universe. Even those reviews I've seen on Ubuntu, or any Linux distribution where bad experiences are felt, is when it comes to the outside expectations from the first time user. You visit a website, you expect flash to be installed. You don't see the initial popup mentioning to you to install the application.  You then plug in some proprietary device into your system & expect it to work. You pop in a DVD & expecting it to work.  You browse the community maintained applications & install them, just to discover it isn't functional. First impressions are presumption that  it's Ubuntu's fault. Though the blame can't be of those who can't legally fix it, or don't maintain it.

 Sometimes you will notice that certain features of at least Linux supported proprietary equipment has limitations which you notice either in other Linux distributions works fine.

Examples:

On older video cards, you had the option at one point to enable desktop effects, but now find it is no longer an option for you.Though if you find in many cases you can troubleshoot & get it operational again.

The case comes down to one thing. Stability.  If the majority of end users tend to run into a problem with one specific feature running a specific hardware. The question you might ask yourself is:

Would you rather have the majority of users to have a good experience, or take a chance getting pummeled with complaints which impact a large majority, so that a few can show off their cool 3D desktop?

 You can just look back at some of the prior releases & see many features which were not implemented during alpha stages, but in following releases. Some would include during version 7.10 when there were new effects included in compiz, were not loaded on default. Even as recent as 9.04 when EXT4 was released. Ubuntu decided to stick with EXT3. They made EXT4 optional for the meantime if you select it under expert mode. Since there was known file corruption issues & stability reported by some users. It was a safer to not take chances. Especially if they are new users.

Even some proprietary drivers still don't fulfil all the capable "uhmph" you would expect your device to do. They also have to make these sacrifices in the best interest of the majority. Intel's Open Source driver is a good example of this. Certain shader options were not available to those running a 64bit version of the driver, in the benefit to give the end user a running stable release until the problems they are addressing could be released in future releases.

64 bit support

Though 64 bit has been around for quite some time, I can at least say the driver side support has been well supported. The only thing I do discover are there are still many applications in which do not have 64 bit equivalents.  Skype for example is one of them. Though there is a repository called Medibuntu which addresses this matter. Yet again, is not initially supported by Ubuntu.