I’ve been a Mac user since OSX since 2004. I can’t speak for the future but I like OSX 10.6
My daily apps are Mail.app, iCal, Safari, MAMP, Jedit, Netbeans, the bash shell, Console, Cyberduck, Filezilla, Colloquy, and of course Renoise.
Other music apps I use are Garageband, Amadeus Pro, and of course dozens of VST/AU plugins.
Firefox and Thunderbird work fine on Mac. I don’t use them. I prefer the native apps.
If you don’t like iTunes you can use VLC. I use both.
I use LibreOffice, not OpenOffice.
I don’t use Jack. Rewire works. We have Soundflower. We have IAC. I’m sure Jack works too but I have never needed it on OSX.
Gimp works, but I own Photoshop (and friends) so I use that instead. You can also try Pixelmator.
Basically a mix of native apps, Java apps, X11 emulated apps and everything in between.
The way I compare Windows, Linux, and OSX: Windows is for power users. You have a thousand ways to “power use” your system yet still have no clue how to edit a text file or use the command line. Linux is a hodge podge of interesting ideas that may or may not work together. A coders paradise. A user’s nightmare. OSX has 2 levels of UI: Idiot, and expert. You cannot “power use” a mac without understanding Unix. If you suck at Unix then you will trash your system trying to “windows” it. However, you can give your grandma OSX and she’ll be able to use it for 5 years because she won’t ever look at Unix, and that’s fine. That’s most OSX users today.
You will be joining a cult. You will be paying more money. But if you like Unix without the configuration hassles, with the added hassle of Apple corporate bullshit you can’t go wrong!