The old forum did have a filter for participated discussions in the sidebar. Unfortunately, this new version don't have that option. You should see the filter for 'My Discussions' there though, a few links below the new discussion button, without having to go to your profile.

These looks great.

I am not 100% crazy about the placement of the legend text. I would probably have moved the entire complex a bit to the right so you can fit the legend text in the bottom left corner, and moved the compass rose either above it, or reduced it a little bit and put it in the right corner.

That's the way of most things. Supporting old software costs money, and if the sales volume is low, it is a net loss. Still selling old maps that are now technically incorrect also causes a lot of confusion in the customer base when the maps don't match up with the books any more, leading to even more support requests and requests for updates. (Of course, it wuld have been nice if they continued their deal with PF and updated it for newer versions, but they had their mapping software in the lineup [Dundjinni], and the atlas maps wouldn't have been compatible with that.)

The FR atlas was a product commissioned by Wizards of the Coast, and the rights belong to them. They where also the ones selling it, not PF, and about the time when D&D 3.0 arrived and the FR maps had some drastic changes in some places, they stopped selling the FR Atlas with the outdated maps (Outdated if you play D&D3.0 or higher that is, for me still playing AD&D 2nd edition, it is highly relevant).
There are lots of nice maps in the FR atlas, but they are from the CC2 era, so they don't look all that nice compared to modern CC3(+) maps [No effects, no raster symbols, and while technically possible, raster fills weren't really used either]

Other products from the AD&D 2nd edition era was the Core Rules products, which included a product called Campaign Mapper, a cut-back version of Campaign Cartographer, which you could use to edit the atlas map if you wanted.

Setting up a linux machine to run CC3+ is just a matter of installing linux, installing wine through the package manager for that linux distro, and then simply install CC3+ as you would on windows (Wine should associate itself with .exe files, allowing you to run the installer easily).

CC3+ should run just fine on any distro (as long as it is recently new/up to date), most of them contain Wine for installing through their package manager (if you manage to find one without easy access to wine, then it would be unsuitable). Personally, I recommend users just use the distributions they are familiar with (and if they aren't familiar with any, I wouldn't recommend they go ahead. Using CC3+ on linux is a good enough option if you already use linux, but if they don't already have a desire for using linux, taking on the effort of learning a new OS for no good reason isn't sensible, and there are some quirks with CC3+ on linux as well)

Generally, CC3+ works just fine on linux, the main issue I've had is that fonts doesn't render the same size as under Windows. This isn't a huge problem when mapping, but it is a problem if you plan to share .fcw files with Windows users (for example if you wish to download an .fcw from the atlas, or contribute one). See the Wine AppDB