Any hints for those that want to upgrade from Delphi 7 (and down) to Delphi 2010?

Converting code to unicode doesn't take that much time in itself as long as you didn't do anything "funny" with your strings. I converted close to 1m lines of code + the database in less than 2 weeks. The guys at codegear did a very good job at doing it a lot simpler.

Your code might recompile in D2010 without any changes (But with quite a few tons of hints/warnings).

The worst problem from the conversion comes from calls to Window's API that were incorrectly done. For exemple, the function GetComputerName that ask you the size of the buffer in TChars(as specified by the API). In Ansi, TChar = 1 byte, so Length = SizeOf. In Unicode, it's not true anymore. Worse, the call to the API might not fail. It will just overwrite some valid part of memory and will crash just much later.

Oh... And there is also those slight differences between Ansi and Unicode in Windows API. For exemple, the lpCommandLine of the CreateProcess is read-only in the Ansi version, but read/write in the unicode version. So using a constant as parameter worked fine in Ansi, but will crash in Kernel32.dll in Unicode.

Overall, it depends a lot on the quality of the code you are working with. Bad code might be very hard to port to D2010. Good code should be pretty easy.

and read the resources that Nick Hodges linked to, they are pretty helpful.

The biggest problems are with 3rd-party libraries and VCL. If they're not on D2010, it can be painful. The Unicode issue comes up if you are doing calculations with the length of strings or PChar arrays, assuming one byte per character. You can usually get away with treating everything as old-style AnsiString / AnsiChar. But then you don't get the benefits of Unicode. If you don't have anything that would be hard to do in Unicode, just do everything in Unicode and you'll be much further ahead than if you have to worry about switching back and forth.

We have created a web page specifically for this very issue:

http://www.embarcadero.com/rad-in-action/migration-upgrade-center

There, you can find webpages, documents, webinar replays, etc. which all cover the issue of migration.

The first thing people say is "I have a huge codebase, and migrating to Unicode will take forever" and almost without exception they discover that "forever" really is a much shorter period of time than they originally thought and that the new features of Delphi 2010 make it all worth it.