I use GNU/Linux at home and at work everyday. While at home, I typically use Google(tm)'s gmail via the web and sometimes with Thunderbird. Google(tm) makes using your email client of choice very easy because they let you access your gmail with IMAP and/or POP access for free. It would be nice if more companies and server products would take the "open and inter-operable to everyone" approach(hint, hint). This is the way things are going anyways as far as I can tell. The only other provider that I know of that allows free POP access is inbox.com.
As for work, I currently have no choice but to connect to Microsoft's Exchange Server 2007(r) product (hopefully this will change sooner or later to something like openXchange or Google(tm)). And Despite the lack of openness of the Microsoft's Exchange Server 2007(r), I am able to use Novell's F/OSS Evolution email client(from Ubuntu 9.10 GNU/Linux) with IMAP to get email but I have to use the built-in Evolution calendar/notes/tasks as opposed to the server based versions. This setup is a bit clunky, but it works just fine for me because I'm not a "power" meetings scheduler and so I rarely need to see other's free/busy information and that type of thing. I actually prefer using Evolution because it's light-weight, nimble, has about the same amount of features, and performs far better and faster on my machine than Outlook(r) does. For some reason, the Outlook(r) 2007 version seems very bloated and taxing in terms of system performance. Besides, there's no Outlook(r) client for GNU/Linux and although I like to get lots of Windows(r) programs working on GNU/Linux with wine, Outlook(r) is not one that I would waste my time setting up that way ;*).
Because I work in a mixed-OS shop, we have several types of Operating Systems: i.e., Solaris, Red Hat Enterprise Linux, Suse Linux, Ubuntu Linux, Windows(r), and Mac OSX, etc. Having these different OSes work together is made more difficult by vendor-locking server platforms (e.g., Exchange 2007(r)) when they are not supportive of open standards and Inter-operability.
For example, we have some users that have moved from Windows to the Mac OSX and some that have moved to Suse Linux. One thing that's always been a problem is moving a user's email from one OS to another. In the case of Mac OSX, there is Microsoft's Entourage(r) 2008 email program, but make no mistake - this is not the same as the Microsoft Outlook(r) product. Even though Entourage(r) connects to the Exchange Server(r) as an email client should - there's no way to import archived email from Outlook(r) (in the PST(personal storage table) format) directly into Entourage(r). So in order to use PST files with Entourage(r), I end up having to have the user copy all their PST archived email from Outlook(r) into their email account on the server. This causes the user's email account to become VERY large, which is unfavorable to say the least. There are 3rd party products that are said to make PST-to-Entourage(r) transfer easier, but I haven't found one that I deem to be worth it's weight in lead. I find this whole situation to be quite maddening. How is it that Entourage(r) does not import PST email when both Entourage(r) and Outlook(r) are made by the same company? Is it entirely political? It's a shame actually.. Really.
And then comes along Ubuntu GNU/Linux 9.10. Specifically Ubuntu 9.10 Karmic GNU/Linux . This amazing and free operating system includes the Evolution PIM by default. So now we can import PST email archives to Evolution from Outlook(r), and it's very simple to do. What's more is that Evolution, after importing PST, can then export your email to the open *.mbx format, which can then be imported by most other standard email client software.
Ubuntu GNU/Linux with Evolution's new drop-in functionality of importing Outlook(r) *.PST email archives makes using Ubuntu 9.10 GNU/Linux at the workplace even easier than before.
I've created a short video to demonstrate the PST import capability of Evolution for your viewing pleasure (see below).