There will NOT be a limit this time around. It will simply be available for a certain amount of time.. Unfortunately I don't know exactly what that amount of time will be just yet but I do know it will be for a while..
But once again... why would you even want to upgrade instead of clean install? Especially when going from a BETA build of Win 7 to the RC.. it just wouldn't be a wise decision in my opinion.. .....................
These scenarios could be a reasonable reason for doing an "Upgrade" rather than a "Clean install"
1) You have some old programs installed
on your previous OS but you no longer have the Install disks -- if you want to continue to use these programs then "Upgrade" is the only solution.
2) Some programs like Photoshop CS4 will probably require a "Re-activation" of the product on a re-install.
If you haven't "Transferred" activation before wiping your old OS you might get problems with "Number of activations allowed has been exceeded" or "Program is already activated on another computer" or similar.
The Final release will probably have enough code in it to appear to your application that you've made a major change to your system and activation will kick in - The pre-RC builds avoid this. A lot of people are also adding memory / disks / video cards at the same time so if you have a product that requires activation ensure you can "Move" it from one machine to another (even if it's the SAME machine).
3) You've installed products from the web plus their updates. Website no longer available -- same problem as 1).
4) You have some VERY complex programs say like SAP etc installed which have an incredibly complicated process of applying "Hotpacks" and fixes. A complete re-install of this type of software is a major issue. -- This problem won't normally be seen by typical "Home" users but it does exist.
5) Some programs just REFUSE to work on W7 even with correct drivers etc etc. These just might work if an Upgrade is done rather than a complete install.
So there ARE genuine reasons as to why an upgrade rather than a complete install can be done - however if you CAN then go for a complete re-install rather than an upgrade.
Note you *might* have to have XP HOME (not PRO) or VISTA installed if you wish to purchase an "Upgrade" version of W7. You can still do a Clean install however -- the old os will be renamed to WINDOWS.OLD which you can then delete. You need to have the old OS installed to start the installation process (although this might change by Retail W7).
The Upgrade W7 version will be a lot cheaper than the full retail version.