Okay, so this title's probably a bit misleading as there are probably a few reasons but as far as I'm concerned there's only one thing stopping my final transition to desktop Linux for complete every day usage.
In my job I do a lot of presenting. I give major milestone presentations on projects, I present to the business on things that are going on, I present in pitches where we are attempting to win new business and recently I've started presenting at conferences.
I would not use my Linux desktop (and I have combinations of Ubuntu and KUbuntu 9.04, CentOS) to present with at all - even if someone paid me.
Before I say why I'll also lay out my Linux credentials. I use RHEL, Ubuntu and Centos EVERY day. All of my home computers are Linux based, I have a Linux PDA, I prefer my Ubuntu desktop for work and I administer numerous Linux (CentOS and RHEL) servers - via command line - all of the time. I've used it for over a decade and am more than happy with it and more than happy to hack on it to get stuff working.
However, there comes a point where I am not going to entrust a complete presentation that our business or my reputation relies upon to Linux's extremely flaky graphics system.
Yes, I know laptop Linux is problematic (but if the rest of the desktop is stable why not my second video out?)
Yes, I know that graphics card support (particularly from ATI) is very closed so there's lots of reverse engineering going on (but again if I can have one video out working why not two?).
I'm not sure why this is the case - I think it's a combination of X.org config and poor tools for configuring multiple screens with different resolutions but it definitely needs a lot of work to go ready for prime time.
I was at a conference this week and I had built my entire presentation in my Gnome desktop using FLOSS tools like Open Office Impress, had a great looking presentation and was legitimately keen on presenting using either my Ubuntu or Centos desktop. After hours of mucking around however I didn't feel supremely confident in just walking up to the podium, plugging in my laptop and "It Just Works"TM. It's just too hit and miss.
I don't generally experience this with Linux in general and Ubuntu specifically although I am aware of other people saying it. For me 99% of the time it does actually just work.
So I defaulted back to my dual-boot Windows partition and presented from that instead. This was the partition that I had considered nuking because I hadn't used it in about 6 months. In this instance though I didn't have any other choice - and sure enough it did just plug in and go.
I still presented from Open Office Impress though (which is a fantastic bit of software I might add!) and I think I was the only one at WDS09 that presented with it (and I'm sure no one could tell I wasn't using PowerPoint or Keynote).
Desktop experience is exactly that - an experience and our experience, particularly when we are doing something social with a computer can affect our mental state quite substantially.
If I'd have taken the decision to present using Ubuntu I would have felt worried about whether my laptop would work and I would have been nervous and probably would have delivered a terrible presentation. In contrast because I knew I wasn't going to have any support issues I felt confident, in control and delivered what I hope was a good presentation to the audience.
Ubuntu are trying to address many of these issues with the Paper Cuts project but that's really aimed at business. Apple have addressed similar issues (hardware compatibility) by having a presenter's kit (which you buy) which provides all kinds of adapters to go from Mac to just about every video input type. Microsoft addressed this years ago from Windows 2000 with a great set of dual head tools that made it simple and a standardised way for vendors to incorporate them and it is extremely rare for it to fail.
Business use is one of the areas that Linux (and especially Ubuntu) has got a real opportunity to shif users across as there are so many other business benefits but users want a single consistent desktop so they aren't going to build on one desktop and present on another - it's too inconsistent.
For me this issue on presenting and graphics support isn't so much a paper cut as it is a gaping flesh wound and it really needs to be addressed.