Don't be disingenuous. Relaunching an application is much faster than rebooting a computer. If you're suffering chronic crashing, this adds up pretty quickly.
I've had very few application crashes. The only times I've been forced to reboot is after major software installs. I've had to do a few logout/login cycles (still much faster than rebooting). This amounts to time saved and less hair pulled.
I'm running a 400 MHz G4 that I bought in Nov 2000 (I think). I've been running X since 10.1.4 was available--a few months now. Some tasks on this system are faster than under 9, some are slower. Some system behaviors are annoying (file renames in the finder, open/save dialog navigation), some are a little weird at first but not necessarily bad (the dock). I've modified the system with a few tweaks from Unsanity to make it more comfortable.
Some of the software updated for X is not really an upgrade, and some is actually a downgrade (Quickeys). There are a few tasks that have become more annoying due to the lack of independent software on par with the OS 9 equivalent, but on balance, I think my productivity is at least as good as before. Some programs are flat-out better: Chimera is a much better web browser than anything available for 9, and it's only at version 0.4, fer crissakes. Office X (I can't believe I am praising it for this) has yet to corrupt any of my files, which was a major time-waster before.