Lets see...I'm looking through my overstuffed program files list...

PSP 5.1 - For some reason, I simply love version 5.1 of Paint Shop Pro. It's ancient at this point, but I'm just so used to all the keyboard shortcuts and the layout that I use it all the time. I even have PSP 7 installed on my computer, but I rarely use it. I also love that somehow, my version of 5.1 is portable.

DVD-lab Pro - I've preached about this program before, and I'll do it again. I haven't met a DVD creation program I've liked more. And believe me, I've tried about a dozen of them. Naturally, I haven't tried any Mac software yet. The thing I love about DVD-lab, though is the philosophy. It's an incredibly advanced program with a lot of pro-level options, but it's simple and straightforward to use without becoming dependant on wizards and crap that bogs down stuff like Pinnacle's software.

THE Rename - A batch file naming utility. I'm sure there are ones available for the Mac OS, but I've been using this one for years (at least four, I think), and I just love it.

VideoReDo Plus, Tivo Desktop Plus, and pyTivo - The first two are my only two essential applications that I paid for (I mostly use free software), and the only two that frankly cannot be replaced by the Mac. Tivo Desktop is on the Mac, but I don't believe the Plus (paid upgrade) version is. And VideoReDo is fantastic for removing commercials from Tivo recordings, mostly because it can re-save into the Tivo format, retaining all the metadata. So at the moment, I have every episode of Lost from this season on my Tivo without commercials, so it takes up about 3/5 of the space. It's great if you need to go back and see something from a previous episode (which we've done many times). I don't know if pyTivo will work on the Mac or if there's an alternative to it, but it's the primary way I get stuff onto my home theater. However, I'm hoping to get an Apple TV, and having a Mac would make it easier to convert video for it.

MP3-Tag Studio 3 - My favorite tagging software. I've tried others and just don't like them. Granted, I haven't tried any for the Mac...

uTorrent - Strictly for Linux ISOs and game patches I really like the slickness of this app, but I used Azureus before this one which was fine, and that works on Mac. Oh yeah, and Revision3 has bittorrent downloads...

Picasa - What can I say? My life is in Google's hands. It's a dangerous dependancy that may bite me one day

Openoffice.org - I believe they're working on a Mac version, though.

GMail Notifier - Essentially I use this every minute of every day. Is there an alternative on the Mac?

Applications for USB peripherals - Just did a quick check. Supported: Logitech MX-1000 mouse, Griffin Powermate, Canon photo printer, and naturally my various external drives (which I'll slowly start to format for the Mac file system of just make FAT32). Unsupported: Sony Ericsson phone suite (no big deal, I'll be moving to a smartphone soon anyway), Casio Disc Title Printers (this is a big one - I use these all the time).

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So, that's my list. I suppose that some of these programs have Mac alternatives, but I just don't think I can give some of them up, and in the case of the Tivo and some of my USB devices, I don't have much of a choice.

I'm also missing a bunch of portable apps that I use all the time like Scanner. Most of them are utility programs, though, that have clear Mac alternatives.