I'm really looking forward to 10.4, but it's hard when reading about what's coming not to say "finally!"...
Enhanced Dock menu — "Quickly set an application or document to open automatically when you login to your Mac — straight from the Dock." Imagine that; they've unhidden the functionality, and put it with its close relative "Keep In Dock".
iCal — "Always know the birthdays of everyone in your Address Book with this automatic calendar in iCal ... Never miss another birthday because you didn’t transfer it from your contacts list to your daily planner. iCal 2.0 automatically displays birthdays listed in your Address Book right in your calendar. And adding or removing birthdays is easy: Make a change in your Address Book and iCal displays up-to-date birthday information."
But will it understand Outlook meeting requests? (Mail on 10.3 won't even show them, even though using telnet(1) to talk to the configured IMAP server shows they're there. Uncool.)
And will it finally check my spelling as I type? How hard is that? One call to setContinuousSpellCheckingEnabled: hard.
Mail — "Mail uses the Safari engine to format newly composed email using HTML." Scary, that one, with it's emphasis on "newly composed". Newly-composed email isn't my worry so much as forwarded or replied to mail, which Mail on 10.3 manages to mutilate most impressively, first stripping most of the formatting, then hard-wrapping at a fixed number of characters. And there's not even the work-around of "forward as attachment". Evil.
But at least we're getting parental controls and slideshows. In Mail. No, seriously.
ksh — "More easily run scripts written for Sun Solaris or similar systems now that AT&T’s ksh is now bundled with Mac OS X." Let the dead bury the dead, dudes. I just hope we also get something useful like GNU make 3.80. And speaking of the dead, a CVS from this century, rather than 1.10 (I wouldn't touch CVS myself, but I need it for other people's projects sometimes).
VPN — "Stay connected to a VPN server when switching user accounts or logging out, and direct all network traffic through the VPN connection." Finally! Like I wanted to have to mess with gateways and routing, just to surf the web or listen to streaming radio when working from home. If I was in to that kind of nonsense, I'd be running Linux.
Tamil support — I wonder if being a "world citizen" means 10.4 will be able to use ISO standard date format? 10.3 can't even get close, for the "long format". Time zones would be handy, too. In Mail, what does "On Jan 17, 2005, at 09:25" mean? Is that now, or was that 8 hours ago in a different country?
Network-based home directories — "Access a network-based home directory even when offline, then automatically sync your work when you reconnect to the server." This might be cool. Or it might require a .mac subscription, like most of the rest of Mac OS' synchronization features. ("Feature" seems too strong a word for something you have to pay extra to use.)
Dictionary — "Quickly find definitions by typing all or part of a word. View the same word in the thesaurus to find synonyms, antonyms and more. Since the dictionary and thesaurus are built into Mac OS X, you don’t even need an Internet connection." I was disappointed this wasn't in 10.1 (the first version of Mac OS I used), since it had been one of the things that impressed me about the NeXT. Better late than never.
The unit converter dashboard widget hopefully means the end of the awful abortion of a converter that's in 10.3's Calculator.
Java — oh, actually, we're still on 1.4.2, but hopefully we'll see 1.5.0 before long.
Don't get me wrong. I love Mac OS. It's the least worst OS by far. It's much better than anything else I've used. But it's not perfect, and in some areas it's still incredibly weak. And Apple being Apple, you've absolutely no idea whether or not they care until something changes.