The thing to remember is that the infamous 'disk too slow' or 'CPU too slow' error messages aren't just some random bug that needs fixing. They are actually warnings that are there for a reason. You'll get them in any DAW - or any kind of audio or even video application - that needs to do a lot of disk read/writes and CPU work in realtime. There is plenty of advice out there on how to optimize your system to get it to perform as best as it can (even in the Logic documentation), but there is obviously a physical limit to how many tracks and plug ins you can use. When you hit this limit, then all the warning is telling you is that your drive or CPU are actually too slow for the task at hand. At that point, there are other workarounds (like freezing tracks, adjusting buffer and other settings, or bouncing subgroups etc) to keep you working. In some cases it might mean that your work is beyond the capabilities of the machine you're using, in which case considering getting a faster Mac and/or faster hard drive(s) is the next solution.
Another thing to keep in mind is that Logic uses a kind of resource optimization process, built in to the audio engine. This means that sometimes you'll get a 'disk too slow' error in some part of your song, but when you play through that part a second time, you don't get the error again. This behaviour is markedly different to how other DAWs work, notably ProTools, where the disk and CPU resources are pre-allocated to guarantee performance up to a pre-defined maximum limit of tracks.. The upside of Logic's dynamic engine is that it allows Logic to squeeze out every last drop of power it can get it hands on, by not doing any processing on tracks that aren't playing audio at a given time. But the downside is that you can get CPU or disk too slow errors at seemingly random places. It can be confusing to see a disk too slow message when playing a certain passage, and then not seeing it again in exactly the same passage later.. leading to people wondering if it truly is random, and a bug. But it isn't a random bug, it's just the way Logic handles audio in an effort to get the highest track count possible at any given time.
Btw, @ fuzznormal: While I agree with pretty much everything you said, you make it sound like a MacBook Pro's internal drive is slower than it really is. Honestly, even if you have put in dedicated SATA II cards or some kind of decent SCSI in your G4, the system buss alone on those old machines is at least an order of magnitude slower than the system buss on any current Mac.. It creates a pretty formidable bottleneck which wipes out a significant amount of any speed advantage the G4 with dedicated drives might have over a MacBook Pro using its humble internal. I (like everyone) used to have a snazzy G4 with a fast SCSI card (I think it was SCSI anyway), and there's no way I could get anywhere near as many tracks running as I can now on my MacBook Pro using the internal drive. Of course I don't usually use the internal drive for audio, but on the occasions that I've had to, it happily chugged out more tracks than my old G4 could, with very rare disk overloads.
