While this isn't strictly iPhone-related a lot of iPhone users are also Mac users so I figured I'd weigh in here a bit. Plus OSX Lion looks a lot more like IOS than anything that's come before it. Besides, it's my blog so there!
Apple released the latest version of OSX yesterday, nicknamed Lion. It's mostly generally positive reviews on-line, though there are some detractors as there always are for things that are new and different. I haven't upgraded yet, but plan to once I know that the applications I use are compatible. How can I tell before taking the plunge? I'm glad you asked. There's a great web site which lists thousands of Mac apps and tells you the status of your favorite applications. And if any are missing you can add them.
Summarizing the reviews would be silly and pointless but if you're thinking about upgrading (and for $30 it's not much of a financial risk.) there is a way you can test it first as I'm going to do tonight. If you're going to buy it anyway it'll cost you nothing and when you're finished you'll have an excellent backup disk. You do have a backup, right? You're using Time Machine? You're not? Oh, boy. Read on.
First, find yourself an external hard drive with at least as much capacity as you're using on your Mac. I'll be using a portable USB disk that I used to carry when I traveled for a living. Next, go to bombich.com and download Carbon Copy Cloner. It's free and it will create a bootable backup of your main disk. Yes, bootable. A few years ago my beloved Macbook Pro's drive died but I ran off of this thing for a few days until I had it fixed. (Yes, Mr Do-It-Yourself had it fixed - it was under warranty.) So, create that bootable backup. It make take a while so let it run overnight.
Next, leave that drive attached and reboot your Mac while holding down the Option button. That's the one that looks like this. The one that says "Option"
When it boots up you'll have a choice of which drive to use for the operating system. Something like the image to the right.
Choose the external drive and let 'er rip.
Once it boots up go to the Mac App store, buy Lion and upgrade. WAIT! (I just wanted to see if you're paying attention). Before you do that you should save the download file. Technically you don't have to as once you've bought Lion you can download it again, but it's a 4GB download so why not just save it?
So, as I said, let the upgrade run. Once it's finished and you reboot just remember the Option key trick and boot into your shiny, new Lion drive. Test, test, test.
If you want to go back to Snow Leopard just boot back into your internal drive. Once you're finished with your testing and have decided to do the upgrade for real I would suggest making a fresh backup on that test drive (Ha! I'm a car geek too! Get it? Yeah, I know: Weak). Just in case. That way if you want to go back you can boot Snow Leopard on the external and clone it to the internal. You probably won't want to, but at least this way you have the option.
Another option, though one I wouldn't recommend, is booting Lion off of the external and cloning that to the internal. Why wouldn't I recommend it? No Snow Leopard fall-back.
And if you're not using Time Machine for backups get another drive for that. Yes, two different backups. CCC gives you a single point-in-time copy so it's good for when your main drive fails or for getting back a file you deleted after your last backup. Time Machine, on the other hand, is good for restoring a file from just about any time since it (sorta - e-mail me for details if you want) makes an image of your hard drive every hour while your external drive is attached. The first time you use it you'll think it's magic.
One more note about CCC: It can do incremental backups so every week or two you should hook up your CCC disk and update it. That way when your internal drive dies (and it will - maybe in a week, maybe in 5 years) you won't be totally screwed, as so many of my friends and family have been over the years. Remember the storage industry's favorite saying: Storage is cheap. Data is priceless.
I'll be doing this testing tonight so if there are any additional notes I'll post them here.
Enjoy and feel free to comment with questions and let me know how your testing and upgrade went!