The current SVN snapshot can be built under Lion but it has some quirks you have to fix first:
1. Edit include/pa_mac_core.h and uncomment the #inclusion of AudioToolbox.h (around line 49).
2. Run ./configure with your options.
3. Edit the Makefile and remove ‘-wError’ from the CFLAGS line.
Now you can type make and everything should build. (Don’t forget to strip PPC code from the generated fat lib (man lipo) if you’re planning to submit to the Mac App Store!)