Delphi 2009 compared to Delphi 2010

It should be very possible to do this migration, and depending on how your code is written, it may either be painful or painless. Unfortunately its not easy to say which until you start the migration process.

The first thing i would do would be to make sure that ALL DFM files are converted to their text representation. This I believe was set to default in later versions of Delphi but as I recall Delphi 3 used a binary format. There should be a utility file named DFMConvert or something in the delphi 3 bin directory which allows you to convert a DFM to text. The reason you will want to do this is to insure that you can read the source if you have to perform a hand edit of the DFM due to a component not loading. Not only are you jumping versions of Delphi, but you also are jumping versions of EVERY component you use and there may be a few incompatibilities that may cause a component to fail loading. I have found if this is the case and you have a "new" version, then use the edit the DFM source directly and compare a test form with the component on it against what your old version contains. Remove anything (or rename) that is out of place and then attempt to load the form again.

As Frabricio mentioned, if you use variants then you will need to make minor adjustments to your uses clause.

The good news is that your code itself should work fine once you get the components/uses clause corrected. If you go directly to Delphi 2010, your only other issue would be Unicode and the compiler does a fantastic job of pointing all of them out to you via errors and warnings.

Better theme support (eg., TStringGrid/TDBGrid now support themes).

Support for Windows Vista and Windows 7, including support for the Direct2D Canvas in Win7 and the Touch/Gesture support you mentioned.

Improved refactoring, including support for refactoring generics.

Built-in source code formatter.

IDE Insight allows you to find things in the IDE itself.

Enhanced RTTI.

Improvements in the debugger, including new custom data visualizers and the ability to create your own. There are two included with source (one for TDateTime and one for TStringList). Also better support for debugging threads, including the ability to name threads for debugging and set breakpoints on specific threads.

The ability to add version control support to the IDE via interfaces. This will allow version control developers to add support directly in the IDE itself.

The help is much better than in previous versions. It's been completely redesigned again, and is much more comprehensive and complete. There's also an online wiki-based version (used to generate the help itself) that you can add or edit.

Background compilation allows you to continue working while you're compiling your project.

As far as third party controls, that's up to the specific vendor; you'll have to check to see if Delphi 2010 versions are available for each of them individually. (You might check the Embarcadero web site, though, to see if they have a list already available; I seem to recall hearing of one... Ah, yes. Here it is. )