Compatibility, network, workgroup access, remote desktop,
I would like to give you a straight answer about this, for the Professional and ultimate, remote PC connection, Home group, Work group, Public group are offer, sharing of files has been improved and it is easy to share file with XP and Vista also.
Anyway for me I decided to go Professional but found that I will have to spend another 15 dollars or so per computer. Microsoft did not advertise that it is required to play DVD if you don't have the Ultimate version that is also not available to the consumer at 50% reduction like their special introductory price for premium and professional and you lost bit locker also with premium and professional version of Windows 7 on this they have been consistent with Vista but the comparison stop there.
If you are in gaming and work same time you will be forced for old game i.e. that work in Vista to probably go dual boot for direct access to the hardware that most of the games are requiring.
Ultimate Vista to Pro is not possible but if you could do it you will see that outside the lost of the codecs for the DVD, you are gaining in reliability or at least more possibility for Backup, domains access etc and network.
If you are in productivity and do not care or only play the most recent games Windows 7 might be what you are looking for. For my case I am satisfy with windows 7 with one disappointment, most or all of my RPG games that were working in Vista will not work correctly without many intervention and tweaking from me and even so it is not full proof when you try that way.
All my programs i.e. MS Office 2007, live office access old printer and their feature are working the way it should or even better then in Vista Printer made by Brother bought 3 years ago MFC-5440CN work now better under windows 7 then in XP or Vista so go figure.
If you want to know will 7 be better and more friendly, YES it is will all my software that are productivity work I could give you a yes with maybe a odd one that will not work but for that you still have virtualisation that is possible if your hardware support it or you could go with sun virtualisation if you hardware does not support it to have XP mode in windows 7.
For a working point of vue 7 will be better then XP or Vista, games maybe not as they involve many proprietary security feature etc that look for specific pointer that might stop you from using then on windows 7.