From Calypso Wiki
What is the rate limits under network properties for?
This is for allocating a set amount of bandwidth for uploading or downloading. By default, this is set to a -1 rate limit, meaning that it is unlimited.
What should I do with the settings for neighbor connections?
It is important to keep in mind that the more neighbors you set this to connect to, the more you will help the network by routing more data, as well as downloading whatever files you've requested faster and getting better search results. The drawback though, is that it will use more bandwidth.
What's the download queue for?
The download queue is to keep the network running smoothly and to make sure you successfully complete your downloads. When a user gets requests for lots of files at once from the same person, it overloads that user and the neighbors he's using to route the traffic to get it to the requester. The queue cuts down on that overload. You have a higher probability of getting the files you've requested if you keep the maximum simultaneous downloads per host pretty low.
Can I search for hashes instead of filenames?
Sure. If you have a hash value of some file that you'd like to search for, then search for this value prepended with a "hash_". Like this:
It should return all the files that are exactly identical to the file you got the hash from. No matter if their filename is different.