I recently got a MacBook Pro, after being a long-time Linux user. I was hoping for a machine where the productivity things would Just Work, and the programming things would be just as slick as on Linux.
Mostly that is true. Encrypting my home directory was just a matter of turning on the option; I know Linux can do it but it had been on my to-do list for months. Email, address books, sleep mode, and many other little things really do Just Work.
On the other hand, I must say that it is not vastly better than Kubuntu. Better, yes, but not vastly better. I still had to install a bunch of extra applications, and I still have occasional times when the machine does not wake up from sleep mode. And as a small point in Kubuntu's favor, Firefox is the default browser, whereas on OS/X you start with Safari but are likely to switch before long.
To find applications you might like, I recommend this blog entry: Free Software for Mac OS X. That site sure makes me wish there was something like a Linux distribution, but for GUI applications. I also like Aquamacs, and I agree with a recommendation from John Weathers to snag iTerm and svnX. For chat I am using Adium, and I like it so far.
The programming works fine. All my old scripts and .el files work the same as on Linux. My sbaz directory worked with nothing extra installed, which is by design, but I had never tested it on OS/X before. I use Fink for grabbing developer tools like jam and subversion. Also, Virtualbox works fine if you ever do need access to a Linux prompt. I still contribute a little bit to Debian, so I need that.
Overall, it's good stuff. I am not sure it is worth the price premium over Linux for most people, but if computers are your job they are well worth looking into.