MJPW  I think 2.5.3 probably still works in most situations, as there are Leopard-specific fixes in it, but the developer no longer makes that version available on his Web site. Since I hadn't kept up with the updates (I think I had 2.5 on my HD), in order to run iVolume in Leopard I basically had no choice but to upgrade iVolume or downgrade my OS. I was satisfied with the new version and the upgrade cost, but I still think developers should continue to make older versions available on their site so people can update or reinstall the software they've already paid for.  
(Version 3.1.1)

MJPW  update: by the time the 21,000 tracks were processed (in about 7 hours), there were actually nine files with the no-tag error. Most of them were downloaded from, shall we say, non-official sources, so they're probably just bad files. Before performing the procedure listed on their Web site, I'd say about 75 percent of the tracks went un-analyzed.  
(Version 3.1.1)

MJPW  oops, meant BSD Unix. you get my point.  
(Version 3.1.1)

MJPW  the actual site is http://replaygain.hydrogenaudio.org, not .com. I visited it and it looks as though it hasn't been updated since 2001.

So iVolume just a wrapper for someone else's code. Code that was made available for free specifically so other people could build their own software around it. You could say that Mac OS X is just a fancy wrapper for BSD Linux and refuse to pay for that, too. If you can do it yourself, that's fine, but most people could not, and if you have any size of music library at all, it's probably worth the cost of a couple of MP3 albums to upgrade to a product that has vastly improved from one version to the next.  
(Version 3.1.1)

MJPW  I thought the upgrade price was steep, too, but then I used it. I used to use the old one and it was just okay--it did an important job, but not particularly elegantly. And eventually the issue with the iTunNORM tags made it virtually unusable.

The new one is ridiculously fast compared to the older versions if you have a CPU that can take advantage of it. I'm on a Mac Pro and it is on pace to power through a 21,000-song collection in about 8 hours, even while using the computer for other tasks. In the old version, you're looking at 3-4 days for the same size library. It also has not crashed once--the old one used to crash every few hours (semi-understandable considering the amount of data being processed for such a long period of time, but still annoying).

As for the iTunNORM tag errors, I finally broke down and tried the process outlined on their Web site, and while it does take time, I didn't find it particularly "painful"--you're just creating a temporary library, deleting it and going back to your old one like nothing happened. And after doing that, I haven't seen a single one of those errors, so it must have worked.

The one remaining caveat is that protected iTunes tracks can't be analyzed. But they can still use the default iTunes SoundCheck adjustments, which are imperfect but better than nothing.

I'm glad this has been upgraded. It's absolutely essential if you listen to your tracks at work or on an iPod and don't want to be changing the volume every time a new song comes on.  
(Version 3.1)