I have an IMac now. It's a 20" one with a 250 gig hard drive, 2 gigs of ram, and a nice dual core 64 bit processor. From a hardware point of view I'm very pleased with it. From most points of view I'm pleased with it. Here a a few things that I notice, coming from Linux:
Lack of a unified package management system - Managing core aplications is a breeze. They're represented by litle icons but are really directory structures containing all needed files and resources. Just drag to wherever you want them to run from or run them from where they are by double clicking on them. Managing non-core things like Perl libraries is not so neat and tidy. Perl comes with the system, but CPAN itself does not in and of itself manage uninstalling. The berkley ports system, called macports, not surprisingly, is available. It is very good, but duplicates things like perl. So you are left needing to keep track of what is managed by what. Core compiler and other development stuff is updated by Apple. Java is updated by Apple. Apache 1.3 comes with the system and is integrated nicely into the preferences panel. If you want Apache 2 you can use macports to install, uninstall, update, etc. it. The same pretty much goes for anything else. I find myself being a bit on my toes all the time as I wonder whether or not I'm using the right system. This is about how I feel on Linux installing something from source that is spread all around the place.
Apple's desire to push products - Apple has a nice (I suppose) email, contact, and storage service called .Mac. Want to share contacts between users on the same computer? Use .Mac, family edition (really an ldap service). The same goes for things like common storage for things like photos or video. Each user's resources are kept on their own. Sharing, with all of the permissions issues that go along with that, is a more complicated and freelance activity not spelled out at all by Apple because they would allow you to avoid .Mac or some other server product. I am technically sophisticated enough to figure out how to set permissions up so that such file sharing will work, but this sort of thing should be built in. As far as I can tell, openldap can be installed easily enough using macports, but there is precious little help from Apple in getting the needed schemas set up so that it can work properly as a .Mac address book replacement.
Too many modifier keys - The bloody apple key is cute and all but ends up adding another modifier to keep in mind when trying to figure out how to do something like select a word or a paragraph when coding or composing a document. Makes me thing of the gymnastic requirements of emacs usage. I'm sorry, but although I am sure there are indeed useful things one can use the apple key for, mostly I find it adds a complexity multiplier. Apple is famous and appreciative for a less-is-better approach in its design. The apple key works against this. Perhaps I'm not "apple" enough yet. It was probably more useful to allow pseudo right-clicking back when Apple only had one button mice (because they were more simple, I suppose, but holding down a key when clicking to simulate a right-click seems to me to be cheating).
Beyond these gripes I am impressed with the excellent indexing and searching capabilities built right into most applications, the usefulness of a truly shared address book, the general way that things just work without trying to tell you all the details like a proud dog, the way applications icons bounce helpfully to tell you, for instance, that an IRC or IM message awaits, that a file is downloaded, and the prettyness of it all. The wide screen real estate is a huge luxury. Using the built in remote to trigger the theatre application is fun and useful. Fast user switching means that my wife and daughter get to share the computer easily. The office suite is good and was much cheaper than office. The list of happy points is long. Most of my gripes are those of someone being able to manage things well in a debian-based linux system. If Apple embraced an integrated the macports system I'd be impressed and happy.