If you're planning to upgrade to Mac OS X Tiger when it is released, you'll still need to check with software and hardware vendors to make sure your setup is 10.4-ready, but PACE copy protection, used in many Mac music applications and plugins, won't be an issue. Andrew Kirk of PACE Anti-Piracy tells us:

The previous mention of PACE incompatibility with Tiger is
incorrect. PACE has provided updates of all InterLok tools to
developers to support Tiger. The latest drivers, that support Tiger
have also been posted to the PACE website.  End users will be lead
through an update to get these latest drivers after they install Tiger.
Specific compatibility of applications will need to be confirmed as
there may be non-PACE specific reasons why the software needs to be
updated for Tiger.

A previous CDM report that implied PACE might be incompatible with the
shipping version of Mac OS X 10.4 Tiger was incorrect. Keep in mind,
10.4 is a major update under-the-hood, so you will need to confirm
compatibility with your setup before installing.