Win32 named pipes and message size limits - is the old 64K limit still applicable?
No, there is no longer any such limitation.
The documentation for WriteFile says:
Windows Server 2003 and Windows XP: Pipe write operations across a network are limited in size per write. The amount varies per platform. For x86 platforms it's 63.97 MB. For x64 platforms it's 31.97 MB. For Itanium it's 63.95 MB.
From this we can conclude that the limitation does not apply to current versions of Windows, and probably only applied to XP when dealing with a network pipe.
We can also observe that if Q119218 was applicable to current versions of Windows, it would not have been archived.
Experimentally, I can confirm that on Windows 7 SP1 x64 a local message-mode pipe can handle messages well over a gigabyte in size. (I started getting "insufficient system resources" messages somewhere around the 1650MB mark.)