The reason why the site could not download your btjunkie file is because btjunkie employ certain security protocols, meaning that the "Download Link" you click for the torrent file is not the actual file itself. It does a subsequent redirect, then the torrent begins to download. I have noticed several sites have this authentication method, and I am not sure how to overcome this issue other than recommending that people download the torrent and upload the torrent file manually. Torrents from thepriatebay, however, work fine via CURL downloads.
Hmm, it worked just fine for me with btjunkie. I'm using a "right click", "copy link address" on the little grey box with the arrow pointing down. That gives me a direkt link to the torrent file, example:
http://dl.btjunkie.org/torrent/The-Holding-2011-DVDSCR-XViD-NoGrp/43585890c419183fe611210d1e90ee9dcf4a01e24430/download.torrent . Pasting that into the form worked.
With regards to the payment system, I am aware that all payments are going to the same bitcoin address. I am already in the process of creating unique wallet addresses for individual users, however, for the time being it is not so big of an issue as you would think. The cost of the download is filesize in GB (to 3 decimal places) * 0.1, then rounded down to 4 decimal places. It is the price of the torrent that identifies the payment, and unless two users simultaneously download a torrent of the EXACT same size, it is not an immediate problem. I plan to transition to a unique-address based solution soon.
This might not be an immediate problem for you, but if there is "the one bitcointorrentz payment address", that might become a privacy issue for users. I would pop this item to the top of your todolist. It's not hard to get a new address for each download and I can't image you having a problem to associate that with the torrent. If you need any help with that, I can help.
Another good point you brought up with regards to multi-file torrents, with many subdirectories. I had considered doing exactly as you suggested and zipping up the whole torrent, but then I felt that some people may want instant streaming access to files contained within. I am still not decided on how I will proceed with this.
Yes please, don't change this. Make zip-file optional if you must. I like it that way for streaming access.
As for your speed, 400kb is indeed VERY slow.
I got around 700 KByte/s which is my downstream cap. (germany)
Had a friend try, he has 50mbit downstream, he got 1590 KByte/s (germany)
Thanks again for this awesome service, please fix the one-payment-address-issue, though.