Same with me too, sometimes I have to go through several restart-cycles just to get it to work, it seems like the drivers are very sticky when they have crashed or locked-up, wouldn't it be great to have a new type of Audio Interface where you plugged it in and it just worked without having to install driver software?, I think that's where Analog has the advantage, it seems to me that when we switched from Analog to Digital recording, all we did was replace one set of problems with some new unforseen ones.
Macs are not immune from Audio Interface problems, a good mate of mine who does audio recording on a professional basis, used to experience problems with his studio setup, he was using a Digi002 with an Apple iMac which was running Pro Tools, every now and then his setup used to emit a loud burst of noise when he booted it up that sounded like white noise, he'd usually end up rebooting his iMac a few times to get it working correctly again, I read somewhere that sometimes Anti-virus software can interfere with the initialization of Audio Interface driver software so that you end up with very glitchy sound.
I reckon it's probably about time I changed over to some Firewire 400 ports with a Texas Instruments chipset, I honestly haven't been too impressed with the performance of my current firewire pots, both of them use a Via chipset.
One thing I did do is download a special app from the Focusrite website that checks my firewire chipsets for compatibility, it's called OHCI Tool, I ran it and it reported that both my Via firewire chipsets were compatible with the Saffire Pro40, but I reckon it's telling me porky pies (lies).