So you've done it, you moved over to GNU+Linux (or you made your move a while ago). Everything works and you're happy with it. Well, for a while now, I've been asked the same question on many occasions, a question I did not previously have a good answer to, "Can I use IrfanView with Debian [Ubuntu, Fedora, etc.]".
Before recently my answer was always "You can't use IrfanView, as it's only available for Windows, and there isn't a good IrfanView equivalent for GNU+Linux." Well, I'm happy to say as of version 2.11.3 that I can now tell people that gThumb is as good as IrfanView, if not better.
I used to suggest F-Spot, no one liked that. Sure it can view and organize images and can make simple edits, like resize, crop, brightness and contrast, but it also started slow compared to IrfanView, and didn't (still doesn't?) play audio and video. Also its Mono dependencies really made F-Spot a pain, because the Mono libraries take up quite a bit of space, 35.8MB for just Mono, does that sound like a small simple image viewer? IrfanView takes up 9.7MB the last time I checked. And gThumb takes up 10.5 here. Free Software advocates also don't like using F-Spot because of potential patent issues with Mono.
When viewing images, gThumb can resize, crop, rotate, adjust colors, enhance colors, equalize, desaturate, invert colors, mirror, flip, and remove red-eyes. gThumb can read and edit metadata, convert images, batch edit multiple images as well, and for organizing your files gThumb also has simple features like Bookmarks, and Catalogs.
gThumb can zoom in and pan images fast as well, and has fullscreen support for viewing both images and video (audio as well, but you don't need fullscreen to listen to music).
The main feature that makes gThumb great is its support for video and audio playback. That's right, gThumb is just like IrfanView it can view and edit images, and play your videos and music as well. When, playing a video there is also a "Take a screenshot" feature which creates a single image file from the current frame of the video.
The best part, most of gThumb's features are implemented by plugins, so if you don't think you need to rotate images, you can simply remove the plugin responsible for that feature. Removing these plugins can make gThumb start even faster. And anyone can develop useful new features for gThumb with a simple plugin.
There is even plugins for burning files to an optical disc, and uploading images to Facebook, Flickr, and Picasa Web Albums. Right from inside gThumb.
And just for the record, gThumb starts in -- well, I'd like to time it, but it starts to fast. gThumb starts in less than a second on my single-core system, I can only imagine what it's like on an Intel i7.
If you want gThumb 2.11.3 on Debian, it's available in the "unstable" repository (sid). As for Ubuntu, the developers have removed gThumb 2.11.x from the latest release, but I suppose the Debian package will work on Ubuntu.
I really feel that with just a little more work, gThumb should replace the "Eye of GNOME" on all distributions. And perhaps become the official GNOME image viewer? It definitely has what it takes.
For more information on gThumb please visit: http://live.gnome.org/gthumb