If each image was 150k, it would amount to only 15 GBs of data. I don't think storage space is as big an issue as number of hits/page refreshes and bandwidth usage.
Thanks for the extra publicity. =] I started this thread earlier today asking for feedback on that concept I had for the Neon challenge, but it fell off the "home page" pretty quickly. In terms of "how I did it", as I described in the comments, it is just a bunch of those "glow necklaces" connected end-to-end.
BTW, there aren't actually 100,000 images on the site. If you look at the About page, it shows that there are 39,958 photographs submitted to challenges and 26,149 photographs in portfolios. The image ID presumably started at 1 and will continue to increment, without ever duplicating a previous ID, for each image uploaded. Unsubmitted challenge photographs and deleted portfolio entries result in that image ID being "unused". But don't forget that all of the printable images on DPCPrints probably take up more space than all the challenge entries combined, simply because of their much larger file size.
