I've been a Mac user for 8+ years and one of my reservations to switching from a PC was, "What Bible software is available on for Mac?" Well, I discovered Accordance Bible software and I've been sold!
I couldn't be happier with their software. Many programs give tons of books (most of which are useless), but Accordance lets you pick packages that have books you'll actually use.
They have tons of commentaries available (which is my #1 reason for using Bible software) and original language tools (my #2 reason for using Bible software).
But here's the coolest thing: they recently released an iPad app. It's free to download, but you can link it your account and download the package of books you've purchased to your iPad. It's genius! I love it!
Anyway, if you've been thinking about investing in some Bible software, this is the one I would recommend to you.
Here's a link to Accordance.
If you pick it up, let me know. I'd love to hear how it's working out for you!