As you might have already seen, Updates 3 and 4 of Delphi 2009 (and RAD Studio 2009 and C++Builder 2009) have been made available by CodeGear. You can read the announcement by Nick Hodges and the official Release Notes. In short, there are two updates because one is for the core Delphi IDe and libraries, while the secondis for the database package, which is installed separately. Download the update from the Delphi Registerd Users area or install it from the IDE ("Check for Updates"), although this might not work properly in Vista.
This is a comulative update you can install over the original RTM of the product of the Updates 1 and 2. You can do a single downlaod of the various updates (there is also a third, a Boost library update for C++Builder) for a total of a whopping 104 MB. Installation takes a lot of time (well over an hour for Update 3, about 5 minutes for Update 4), as many modules are first removed and later reinstalled.
The list of bug fixes are here for Update 3 and here for Update 4. As you can see there are dozens of fixes, including some relevant ones in the database and compiler areas (including generics). Those listed are only the errors that were publicly reported. If you use Delphi 2009 (or C++Builder) I strongly recomment you to install these updates.
Now, the question I have for Nick is, "Why the delay?" Just joking, as he specifically mentions in his blog post this is a question he cannot reply to. Hope that now that this update is out CodeGear can go full steam ahead working on Weaver, the next version of Delphi.