What I Dislike About Linux/PPC
Linux/PPC has its problems too. If you've tried it and hated it, that's fine. It's not for everyone. I find its problems much less frustrating than Mac OS X, so I use it.
Most of my frustrations with my current system are due to its relative unpopularity in a world dominated by x86-compatible machines. For the most part, running only free software ameliorates this issue. (Of course, there are very few opportunities to run proprietary software.)
Lack of Pre-Built Applications
The Linux kernel runs on many, many architectures. For desktop users, there's one architecture worth worrying about: x86 compatible. (Okay, there are 64-bit processors too, but they're hardly as different as PPC is.)
If I wanted to run a binary blob video driver (I don't, but some people do), what are the chances that anyone would think to build a version for Linux/PPC? Bad example? Try Java. I can install IBM's JRE 1.4.2, but nothing more recent from Sun. Java 5 came out in 2004. (People tell me that I can get newer versions, but I'm sticking with my packaging system. Life's too short to manage dependencies manually.)
The same rule applies to larger free software packages such as X.org and OpenOffice.org. I don't really want to compile the latter myself. (This isn't a complete loss; MySQL AB does provide Linux/PPC binaries, in part due to a bug I filed.)
Perhaps I'd have better luck if I switched to an Ubuntu/PPC distribution, but as Apple stops shipping PPC machines, there will likely be even fewer people using the platform. The smaller the target audience, the less testing there is and the longer it takes for a distribution to mark updates as stable.
A related issue is that a lot of software makes unportable assumptions about memory layout. That is, which bits in a piece of memory are the most significant and which bits are the least significant?
A few projects that perform high-performance bit-twiddling code (think cryptography or image and video editing) broke on my machine with upgrades, as the developers of those projects made unportable assumptions about endianness. Fortunately, this hasn't been a problem in over a year, but it does point out a further problem with running a niche platform.
This isn't all bad, however. The likelihood of having a remote exploit due to a buffer overflow is low; how many attackers are capable of writing Linux PPC shellcode?
Sticking with software for which I can get and modify source code does have an advantage here if the software is important enough that it's worth my time and effort to make it work. (Don't laugh. I've done this more than once.)
What I Miss About Mac OS X
My list of annoyances with Linux/PPC is short. My list of annoyances with Mac OS X was more substantial. Those aren't the only factors in my decision, however. By switching, I gave up some nice features that I miss. They aren't worth switching back, but I do miss them.
I have never used an operating system or piece of hardware with better networking support than Mac OS X. I've looked for similar tools for Linux, but I haven't found anything I like better than a little shell script I wrote myself. That doesn't mean they don't exist -- it's probably incomplete driver support for my hardware.
Still, this is an excellent feature on Mac OS X and I miss it.
Full Driver Support
Though I hate binary drivers, it's difficult to argue with working hardware. All of my hardware works sufficiently under Linux (including my scanner, which is more than I can say with Mac OS X), so it's not a big issue.
Still, having to wait for full and fully-open video card, modem, and wireless card support was frustrating. It's the fault of the manufacturers of course, but I do wish I had had full support from the day of purchase.
Easy Remote Displays
For the most part, I have never had any significant trouble connecting my laptop running Mac OS X to remote displays. Occasionally I had to change the resolution and refresh rate, but I expect that as the properties of remote displays are often different.
I have never tried to do the same under Linux, though I keep meaning to do so. I suspect that it might be easier with newer versions of X.org, but it has not come up yet.
Bonjour and SubEthaEdit
I've never used SubEthaEdit, even under its previous name. It looks like a nice tool. It may never replace Vim for me, but collaborative note taking is convenient in certain circumstances.
I will never switch to a different platform solely for a text editor, though.
Having multiple applications aware of zero-configuration networking via Bonjour is a very nice feature, however. I would like to see the same on desktop Linux -- especially on laptops.
Some Parts of Mail.app
Mail.app had some nice features and some frustrating features. It worked very well in offline mode, at least for me. I do miss the ability to disable one account. That is, it's nice to disable checking for my work account at 5:01 p.m. on Friday afternoon and not enable it again until 8:59 a.m. Monday morning.
... but I made my own.