This was a bit of a "duh" moment for me, but probably worth mentioning, despite being a "Captain Obvious" post.
I'm a big fan of what Apple's doing with Xcode 4, but in my opinion it's just not ready for production use yet. I'm using it for the book and occasional forays, but not for regular client work yet. However, I also run my machine using the 64-bit kernel, which means I can't use Shark without rebooting. I've been really looking forward to the Time Profiler template in the 4.0 version of Instruments as well as the two new OpenGL ES templates and the Energy Diagnostics template.
But, while grumbling about their lack in the current release version of Instruments, it struck me: you don't have to launch Instruments from the same folder you launch Xcode from. You can launch Instruments separately and attach it to a running process in the Simulator or on an attached iPhone. That means, you can launch Instruments from the Xcode4 folder instead of from the Developer folder. This allows you to develop and debug with the less-shiny-but-production-ready Xcode 3.x and also use the new Instruments templates like Time Profiler, OpenGL ES, and Energy Diagnostics.