Adding iOS UI elements of OS X means lots more small I/Os, the kind that disks do poorly and SSDs do well. Don't buy a new Mac without an SSD or you'll regret it!
All iOS devices run on solid state storage. Mac OS is including many iOS features - such as remembering all open windows and documents - that require many small I/Os for both data and metadata. Finally, Lion performance - boot up, file access times, page swapping, context switching - all suck using a 7200 RPM drive.
And if you're running FCP X, forget it: booting up on a disk takes minutes from what I've seen on an 8-core Mac Pro.
How much suckage? Let's just say that my 1.86GHz Core Duo 2, 4GB MacBook Air with a 128GB SSD outperforms my 3.4GHz quad-core i7, 16GB iMac on ≈90% of the work I do. And it is more stable.
Apple buys ≈50% of all flash production. This is the year that SSDs become standard on all MacBook Pros - or whatever the Air-like models are called - except for low-end educational models.
Lessons learned I have a front row seat on this issue thanks to a 2011 Thunderbolt iMac. At purchase I knew that Apple underconfigures storage and that an SSD - all other things being equal - was the right choice. But the $500 added cost - a 25% increase - scared me off.
So I went with the stock 1TB SATA drive. After all, I thought, I can add an SSD later, for a lot less money.
Big mistake. My satisfaction with the iMac is as low as any Mac I've owned. If it weren't for the big 27" screen, it would be on Craigslist.
Will I add an SSD? Cracking the iMac case and removing the hardware required to add an internal SSD is non-trivial. While SSD prices have dropped nicely - and I expect further drops in the next few months - I still haven't pulled the trigger.
The Storage Bits take Apple is all about user experience. And the user experience on Lion with standard disks stinks.
All Apple notebooks - 2/3rds of the Mac business - will go SSD this year, or they should. To meet price points, low-end iMacs and Mac Minis will stay with disk drives, but you'd be nuts - or broke - to buy one.
Once MacBooks go all SSD, the performance difference between them and most Wintel 'books will be obvious. Expect more envy from cheap Wintel notebook users.
Comments welcome, of course.