As a guy who works in a cross-platform shop, one of the clear advantages I see for Solaris over Linux is DTrace (please don't kill me everyone). SystemTap is great, but the complexity required to get started on SystemTap is much greater than DTrace.
DTrace has a set of static trace entry points. While it could lack some flexibility because of that, it is very well documented and relatively easy to understand. SystemTap seems to require too much specific knowledge of the kernel and how its written to be used by the semi-casual administrator. Perhaps a set of core SystemTap libraries could resolve this?
In addition, DTrace seems to allow much better profiling of user-space code. What I'd love to see in SystemTap is functionality similar to Google Performance tools. Allow me to instrument userspace code without having to modify that code.