Ctrl-PgUp/PgDn can be used for switching between tabs in most gtk user interfaces, but in soundnua this does not work correctly: it also takes the focus away from the tab control itself (and selecting something inside the tab?), so you can't use it to cycle between tabs quickly.
ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: unity 5.8.0-0ubuntu2
ProcVersionSignature: Ubuntu 3.2.0-23.36-generic 3.2.14
Uname: Linux 3.2.0-23-generic x86_64
ApportVersion: 2.0.1-0ubuntu1
Architecture: amd64
CompizPlugins: [core,composite,opengl,compiztoolbox,decor,vpswitch,snap,mousepoll,resize,place,move,wall,grid,regex,imgpng,session,gnomecompat,animation,fade,unitymtgrabhandles,workarounds,scale,expo,ezoom,unityshell]
Date: Thu Apr 12 00:50:21 2012
EcryptfsInUse: Yes
InstallationMedia: Ubuntu 12.04 LTS "Precise Pangolin" - Alpha amd64 (20120103)
SourcePackage: unity
UpgradeStatus: No upgrade log present (probably fresh install)
That's not specific to the sound capplet, if you use tab to focus the notebook widget it works, the same issue happens with other capplets (keyboard, mouse, ...)