The distribution used at my work is CentOS. I think that's mostly because we use Red Hat on our servers, and of course CentOS is exactly equivalent to Red Hat. By default, it only installs Gnome with Red Hat's bluecurve theme. I always preferred KDE, so I installed that and use a slightly tweaked version of its modern theme.
So how easy or difficult is it to use Linux as my day-to-day OS? Let's take a look at some of the daily tasks I use my computer for.
Web browsing -- This is pretty good on Linux. CentOS came with Firefox 1.0.x. I updated it to Firefox 1.5. This is exactly what I would be using on a Windows or Mac system. It seems a little slower on Linux, and there are more rendering abnormalities. So I also installed Opera. This runs very fast on Linux, at least as fast as it does on Windows. There much fewer browsing quirks. I love all my extensions on Firefox, but it is tempting to switch to only using Opera on Linux. It is a far superior browser on Linux.
Email -- CentOS comes with Evolution. I'm not a fan of this program, so I installed Thunderbird. This works great, just like on Windows. Seems as fast as it is on Windows, unlike Firefox. The only weird thing is that I can't seem to get its email notifications working. I actually think that not having email notifications is kind of a blessing, since it is easy to get distracted and become less productive because of email notifications. So I'm not too upset with this. I also installed an open source GMail notifier. Unlike work email notifications, there is less downside to getting personal email notifications. This worked great, but did take a little configuration. It also seemed a little dangerous that I stored my GMail password in plain text in a configuration file.
IM -- Gaim is great. I've often thought of using it on Windows, but it totally rocks on Linux. I'm actually using my AIM account for the first time in a long time. A couple of years ago, this didn't work for me on Gaim because my AIM account was actually a .Mac account. Now it works great. I log in to it and my more heavily used Yahoo and Google Talk accounts. Only complaint would be that the Google Talk account should be able to generate GMail notifications, but I got the GMail notifier mentioned above to make up for that lack of functionality.
Development -- This was the easiest thing. I do most of my work in Eclipse, which works great on Linux. The only slight issue came from CentOS installing JDK 1.4 and putting this on the path. This could not be upgraded in pace to JDK 5, which I had to have for Eclipse to run (and to actually do my job.) So I installed it separately, and modified my .bashrc and .bash-login files to modify my path with the proper version of Java. No problems with things like Apache, Tomcat, or MySQL. I did have a weird problem installing DBD::mysql from CPAN, though.
Desktop Publishing -- Here's where things got tricky. I used to produce a lot of technical documents with MS Word and Visio. Open Office's Writer program works pretty well. Its UI leaves a lot to be desired, but I'll probably get used to it. It is slow to load, but pretty responsive after that. As for a Visio replacement, Dia claims to be one. This program seems awful though. It's UI makes Writer look nice, and everything about is cludgey. This was inadequate for producing software documentation. I could do some basic UML, but nothing very advanced. So I downloaded the free version of Visual Paradigm for UML. This is a nice program. It's more equivalent to Rational Rose than to Visio, so it has a lot more advanced features. I had a little bit of trouble getting started with it. Maybe if I was more used to Rose, it would have been more intuitive. But in the end, I was able to be productive with it. I may have to get my company to buy the more advanced version of this program. However, I had some serious issues with printing from any of these programs. I had no problems with printing from Firefox or Thunderbird, but for some reason the Open Office apps have issues.
Music, movies, photos -- My workstation is actually a server. Thus it does not have a sound card and only CD-ROM drive. So I haven't really been able to do much with music or movies. As for photos, I installed Picasa for Linux. This uses Wine and seems to work great. I did manage to crash it mysteriously once, but I wasn't doing anything with it at the time and restarted with no problems. It is surprisingly fast. I did need to do a little bit of image editing, and busted out The Gimp for that. I experienced what all Photoshop users experience when they use Gimp -- everything seems like it is in the wrong place. There is some logic to how Gimp organizes things, but it is difficult to get used to. Like the Open Office apps, it is also kind of an ugly UI.
So there you have it, desktop Linux. It is working just fine for me. Of course I am a programmer with prior experience with Linux. Most of the "advanced" things I did are things that most people wouldn't need to bother with. I do a lot of weird things to Windows as well, like modifying environment variables and disabling default services. So I don't think I did that much more on Linux. Maybe it really is ready for the masses...