When installing any combination of ArcGIS products (Server, Desktop, ArcSDE) on the same server or development box in Windows, the process is needlessly long and painful. You have to finish installing or patching every single product to use anything without worry. Also, installers take considerable time checking for available space. ArcGIS is the only Windows installer that still does this step, and it is particularly bad if you are troubleshooting a broken service pack install.
1. The installer should always just report how much space is needed. If necessary, show the free space on local disks and let the user continue or cancel. This will cut out 10 - 30 minutes of time on some systems.
2. Set up one installer to install of the core and shared elements - don't make a customer wait while the same components is being installed or verified by both server and desktop. Then you can reduce the size of the server and desktop specific components. Do the same for patches and service packs. It's working well for the ArcObjects SDK.
3. Design installers to allow for a repair rather than requiring the time-consuming process of uninstalling and re-installing everything.
4. Fix the uninstallers so they actually clean up all registry entries and files, so a re-install doesn't fail.