I'm sure people having issues are blaming FCPX for problems caused elsewhere in their system. I know that seems like a personal insult along the lines of "You don't know how to run a fast and stable system!".... but that's probably the truth...and the truth hurts sometimes.
In my opinion, (and that's all it is) FCPX is very stable, very fast and every bit as professional as FCP7, Premiere or AVID MC6. I've worked on NLEs since Speedrazor on the PC, moving up through Premiere, FCP4,5,6 and 7 before FCPX. I'm not an Apple fanboy... i love my Apple computers, but i hate iPhones. I use a Samsung and i have both an iPad and a Google Nexus.. so don't go assuming i think the sun shines out of Apple's butt...cos i don't. I just like forward thinking and efficient systems that allow me to bring my creative ideas into the world with as much speed and as little interference as possible.
So...to the tips for a stable and fast FCPX set-up:
1. Install the latest version of Mountain Lion. - Yes, you can force FCPX to work in Lion, but don't expect the best performance...it runs better in Mountain Lion.
2. Install as much RAM as you can afford. FCPX uses all available RAM...so load it up. Don't skimp on cheap RAM. Buy Crucial or something similar.
3. Keep a lot of free space on your system drive. FCPX uses free HD space on the system drive for virtual memory. For even better performance, make your system drive an SSD.
4. Avoid USB2 or FireWire400... they are not fast enough. Did you know that having a FW400 drive anywhere on your system will slow ALL your FW800 drives down to FW400 speeds??
5. Use separate FW800, E-Sata or Thunderbolt drives for Projects, Events and Audio. Do not put them all on the same drive. Separate partitions do not count.
6. Transcode everything to Pro Res when you import into FCPX. Also tick Proxy (as well as, not instead) if you want to work with complex compositing or multicam clips at high speed.
7. Install a copy of Event ManagerX to stop FCPX from loading all your projects and events all the time. It speeds up boot times and keeps things quick.
8. Keep background render turned off and just manually hit render each time you want to take a break. It will still play a lot of stuff in realtime, but you won't get the spinning ball of death if it starts to render something complex while you are still working.
9. Don't confuse FCPX with huge jpegs or other stills. Re-size to the size you need before you import them. They can be bigger than you need for cropping into, but don't use loads of massive stills unless you need to.
10. Repair Disk Permissions in the Disk Utility often. These get out of whack quite easily and cause all kinds of issues. Power off your Mac properly often too...don't just let it sleep. A proper restart is good for the RAM and the HD stability.
So, there it is. Run a clean and efficient Mac... don't clutter it with crap. Don't skimp on cheap RAM, a good Video Card helps... mine is the AMD Radeon HD 6970M with 2048MB. Don't use external peripherals you don't need..they all slow things down. Eject drives you don't need.
If you system falls over when you work on large (long) projects, there's something wrong. Check your footage. A corrupt file can cause havoc in FCPX... make sure all the footage icons (QT) show a min thumbnail of the video. If they don't, they could be corrupt.
For safety, make a duplicate of your project on a separate drive. Update it often to avoid tears later.
If you've read my blog for a while, you'll know i took some time to warm to FCPX. It wasn't good to begin with...but i kept checking back and from a few versions ago, it's been sensational. I had to open FCP7 recently to work on an old project. It was like putting on an old favourite pair of trainers only to realise that they look ridiculous and give you blisters. The FCPX team have done wonders. I can't tell you enough how much you should try it. I'll be sticking with it for all my features from now on.