I must be about the only one who understands Axel when he says he's not going to add a thumbnails feature (never say never, anyway). He sounds a bit stubborn sometimes, but in my opinion, he's right.
The only way to have thumbnails load fast is by keeping them in a database, like ACDSee, Picasa and others do. Otherwise, you have to build them every time you open the thumbnail view, like irfanview does, taking quite a long time to load them, if there are many pictures in the folder and they're big. Taking care of the database (keep it updated, not corrupted, etc.) is not easy, you must keep it somewhere (pictures folder, app settings folder...), you have to build it some time (the first time you run the app, the first time you navigate to a folder)... It's a real burden.
Now, Windows already has a built-in thumbnails view, which, from Vista on, is rather complete, and database based. You can see a lot of info about the pictures; you can resize the thumbnails, you can run your favorite viewer with a double-click... So, why bloat the software with something that's already in the OS?
That said, I sometimes miss a thumbnail view too, because I'm used to it from having used it for years. But I much rather have a program that loads quick and lets me review my pictures really fast. Anyway, if I ever need the thumbnails, I can run any other program that uses them.
I guess this will be an endless discussion, and every now and then someone will come with "why isn't there a thumbnail view?", so here's my opinion. After all, everyone has his/her needs, so this program, as well as any other, will be useful to some and useless to some others. That's life. I personally find it awesome, and I really think that a thumbnail view wouldn't make it any better.
Just my 2 cents.