Firstly, from my first glance at your forum, it isn't the most attractive site, especially for a site which should be (most expectantly) be showcasing stunning, wonderful wallpapers.
Also, when I scroll down the page, all I can primarily see is an array of... girls. I know that some like looking at those kind of things, but I assume this site is for any age. Seeing a majority of half-naked women kinda put me off and gave me the impression most of the sigh would contain such wallpapers.
Continuing from the above point, to save a lot of time for yourself you could stick to one/two main genres for the wallpapers which are primarily submitted. It won't only save time, but I think it'd also help you scope a better audience when you're advertising.
Another suggestion is that you try and fill every category with content - I am interested in gaming wallpapers and all I see is one wallpaper. I understand that you'll be wanting to get other users on the site to submit their own wallpapers, but I think before you do that you need to supply the categories with a fair amount of wallpapers.
That's all from me for now. Hopefully you can consider the above points and extract these into the future of wallpapr.org. 🙂 Best of luck.
Oooh, this one has caught my eye! I'll say a few things about it!
Pros:
I like your theme. Simple colors, simple contrast, curved navigation bar. Very very simple and useful. Love it!
Nice, simple tool. I don't see many decently looking wallpaper sites out there. Most of them are just a clusterf**k of pictures. I could actually see myself using this site one day.
Cons:
Too many girls... Okay, I know you guys love looking at hot, sexy girls, but I can guarantee you that there is a lower number of men who set women as their background. Why? Because it's usually football, friends, or video games. Try to get a few more sci-fi, football, etc wallpapers. Diversity!
I hope I helped a little! If you're interested in some more feedback, feel free to request an official Forum Promotion Review HERE.