Our experience with Windows 7 application compatibility has been very positive.
The only small hang-up is our very old accounting/ERP system. The only way we could get it to function was by turning off user account control. We had the same issue under Vista, so this was not a surprise to us.
A somewhat larger problem had been hardware compatibility, especially for printers. The printer compatibility problems are even more problematic on the 64-bit version. For example, we have a couple of HP Color Laserjet 2600n printers. These are vista-era printers. Under 32-bit Windows 7, no problems. But under 64-bit, the printer will work fine via USB, but becomes very difficult to get working over a network.
However, all that being said, nothing has been show stopping. We are bringing in all new computers with Win 7 factory installed.
Here's an aside on app compatibility -- sometimes "run as administrator" just isn't enough.
In my off-time I am a PC gamer, so I 'play' with my computers at home quite a lot. I just can not list the number of games and other programs that won't run under Vista/Windows 7 until User Account Control is disabled. I don't recommend turning off UAC to most folks because the security benefit it provides is well worth it. UAC is fundamentally behind much of the compatibility grief with older software. So if you absolutely need to run something, try disabling UAC and hope you stay safe on the net.
Either an application is compatible with Windows 7 or it's not. Few (if any) applications should be dependent upon features found in "Professional" which are not found in lesser versions of Windows 7.
I assume they chose "Professional" because it's the least feature-rich (and least expensive) edition which is designed specifically for business networks utilizing ADS. Kind of a "lowest common denominator" for business apps.
Maybe the point is that if they are running under Windows XP Professional now, then it may 'require' Windows 7 Professional.
Let's be honest though, the NT 6.x kernel was designed specifically to enforce Windows XP certification standards. Programs which were certified to run under XP should work fine.
Sadly, many applications written for XP ignored Microsoft programming standards and never sought certification. The problem was even worse for in-house developed programs and drivers.
Microsoft did not enforce those standards because they were more concerned about supporting legacy applications than they were about protecting the integrity of the operating system. That has all changed.
Microsoft paid a high price (and is still paying a high price) for not enforcing standards under XP and then not driving home the point with its ISVs during the Vista launch.
Undoubtedly, late adopters (those still on Windows 2000/XP) will continue to suffer until all of the software has been upgraded. (But Microsoft will be the one getting the black eye!)
Five years ago I got my first Palm, the Treo 650 -- solidly built (it's still working perfectly), stable platform, lots of great apps, free and paid.
But the single-tasking became a problem in a fast-moving world, and Palm was too slow to address that deficiency -- especially outside the U.S. where Windows-based Palms weren't readily available. So came the move to Windows Mobile on HTC -- which had to wait until 6.1 for decent message threading, and whose hardware is nowhere near as well built.
Time to upgrade again, so I was looking forward to the Pre, having monitored its release a year ago. But, after a year, there is still no real take-up by developers. On top of which webOS doesn't support my (coerced) investment in Windows Mobile apps. In any case, the Pre has not been type-approved in South Africa yet.
Hmmm... hopefully HP will take the highly-promising webOS and make use of its marketing muscle and worldwide reach to increase turnover. This would ensure that Palm doesn't die out.