...plan to incorporate them into your deployment images. Otherwise you can either leave users to download and install them or ban their use altogether. In which case, you should look at encouraging the use of alternatives — such as Outlook for email, calendaring and contacts — that are easier to manage and support.
One last major issue, and one you should address as soon as possible, is how you're going to activate your Windows desktops.
In a small company you might be able to do this manually — especially if you're deploying retail copies of Windows 7 or an OEM version preinstalled by a computer vendor. However, most businesses will have some kind of volume licensing agreement and will want to automate the activation process as far as possible. Two volume activation technologies can be used here: Multiple Activation Key (MAK) and Key Management Service (KMS).
Either or both can be employed, and neither presents any major technical challenges. However, there are a couple of practical considerations: MAK activates systems on a one-time basis using Microsoft's hosted activation services, while KMS customers can activate systems themselves from a server on their own network.
According to Microsoft, KMS is the preferred approach and should be used by the majority of customers migrating to Windows 7; it's the easiest to automate and everything occurs within the secure customer environment. It does require a server to host the KMS service, but this doesn't have to be dedicated, and there's also support for Windows 2003 as well as later 2008 platforms.
MAK is better suited to smaller companies or individual standalone machines and those disconnected from the network. A server isn't required, but a Volume Activation Management Tool is included in the Windows AIK (Automated Installation Kit) to help with the process.
Other practical issues include whether you go for a staged rollout or migrate all of your desktops in one go. The latter should be avoided, except in small organisations, and you should try to get each stage of your migration working correctly before you move onto the next, incorporating the lessons learned as you go.
Likewise, it's important to anticipate the problems that will, inevitably, arise. For example, you'll need to deal with disconnected systems separately and have a proper strategy for branch offices where bandwidth will dictate what's possible — you may have to schedule site visits. And don't forget your mobile users: it's not straightforward to deprive road warriors of their notebooks, even for a few hours.
And one last bit of advice. If you haven't done so already, subscribe to Microsoft's TechNet service: it's packed full of resources designed to make your Windows 7 migration as smooth and successful as possible.