We like to keep systems upgraded here and have an all 2008 Server Standard (with the exception of a few systems in which the vendor only supports 2003R2) fleet.
For the most part, none of the systems are particularly complex, nor do we have an overwhelming number of systems. A bunch of AD/DNS/etc. systems, some SQL Server boxes, various non-mission-critical servers, and an Exchange server.
Virtualization & HA is all done within VMWare ESX Server so we don't really find the Hyper-V stuff or OS-based clustering all that interesting.
Given that we're all comfy and cozy on 2008 and aren't really taxing the systems we have is there a real need to spend the person-power to upgrade to 2008 R2? Should we just wait the n-number of years until the next major release of Windows Server? Assume all of our hardware is relatively new and is expected to be in-service for the useful life of the hardware.
Thanks!!
EDIT: We're running XP Pro on 100% of the desktops but as they age out will be replacing them with Win7. Our group/domain policy is very simple and (in our testing) wouldn't require any changes for Win 7. No foreseeable plans to massively change our office/workstation/etc. topology.
Added note:
2008 R2 does NOT need new CALs (that's really the purpose of R2 releases - they can use the previous version CALs. If you wait until the next release of server, you'll have to repurchase all your CALs (though you'll have to do that anyway if/when you go from 2008 R2 to 20xx).
For all intents and purposes, 2008 R2 is the next major release of Windows Server. Despite the confusing marketing name for it, it is effectively Windows 7 Server. It's not a simple feature addon like R2 was for 2003. It's a full fledged OS revision complete with schema updates for Active Directory and new domain functional level option for domain controllers.
That said, if what you have is working, you certainly don't need to drop everything and rush to 2008 R2. Take your time and migrate as it makes sense to. If you've got the licenses and you're bringing up a new server, there's no real reason to not put R2 on it.
We have a fairly extensive ESX environment as well (still at 3.5) with about half and half of 2003 R2 and 2008. I've tested 2008 R2 on a couple VMs now and it actually feels a bit snappier than our 2008 VMs. Most of our VMs are pretty small and only run x86 versions of Windows since they don't have gobs of ram. I figured I'd be paying a slight penalty for needing an x64 OS for 2008 R2, but I've been pleasantly surprised so far. With the addition of .NET support to the Core versions of the OS, we're probably going to be able to migrate some of our web servers to Core versions as well.
I recently upgraded all of my own servers to Server 2008 R2 and while it was mostly painless there are a few things I'd like to point out.
I, myself, am loving Server 2008 R2. It has a number of features that make life just a little easier. Less UAC prompts and better power management (Core parking!). The only drawback has been that it is now 64-bit only. So I've had to keep a few Server 2008 RTM VMs around because some of our software uses 32-bit drivers. Also, things like Team Foundation Server require the web front-end to be a 32-bit box.
The best thing you can do before going forward is to research all of the software you use and make sure that it is 64-bit compatible and that the vendor will support it on a Server 2008 R2 box.
Also note that you cannot upgrade a 32-bit system to 64-bit so the only systems that can be upgraded are your 2008 RTM (and SP2) 64-bit boxes.