What the fuck is memcache? Is this available on cloud hosting too or is it just used for cheap, shared hosting?
Memcached keeps a copy of your prosper database in the server's RAM. This data is usually pulled directly from the hard-drive via mySQL. Memcached sits between mySQL and Prosper's php code, greatly reducing the hard-drive access bottleneck.
Without Memcached:
Hard Drive -> mySQL -> Prosper
With Memached:
Hard Drive -> mySQL -> Memcached -> Prosper
There's another type of cache for PHP called an opcode cache that stores compiled versions of your most commonly used php scripts in memory. PHP typically interprets each script every time it's run. By compiling the script the first time it's requested and storing it in memory for future use, your php scripts will run much faster. There are a few to choose from, I like APC cache. This works with your current code, so you don't have to change anything, just install the opcode cache on your server.
Don't waste your time with shitty hosting, ie. Dreamhost, get yourself a serious VPS from day one. If there's any confusion, a VPS and cloud hosting are the same thing. Shared hosting was cool when you were getting started, but if your serious about these internet moniez it's time to upgrade your shit.
VPS (Cloud Hosting) + Apache + PHP + APC Opcode Cache + mySQL + Memcached + Prosper and you're server will be fast. Faster page loads, shorter hops, and more conversions.
If you get really big you'll want to setup a reverse proxy like nginx, lighhttpd, squid, or varnish to balance the load by routing traffic to multiple webservers. Each of these webservers connects directly to memcached so that data and sessions are kept consistent across servers.
Finally, grab an SSL certificate over at Godaddy and setup your prosper server on HTTPS. Some affiliate networks only allow tracking over HTTPS and it's the most effective way to cloak your server's url, as there's no referrer passed over HTTPS.
Also... blackhat cookie stuffing, ninja optimization, se0, adwerdz, secret guru traffic sources, mee-j-dia buys, spiders, the google, and jamoooola.
Speed up your servers bros.