downloading
You can get the latest release at my mediafire page.
I release a new version every Wednesday at 8pm EST and write an accompanying post on my tumblr. If you have an rss client, you can use this to keep up.
installing
If you want the easy solution, download the .exe installer. Run it, hit ok several times.
If you know what you are doing and want a little more control, get the .zip.
Hydrus stores all its data—options, files, subscriptions, everything—entirely inside its own directory. This means it needs access to itself, so don't put it in Program Files unless you are willing to run it as administrator every time. I usually go for something like D:\hydrus.
Also, make sure your hard drive has enough space for what you intend to store. If you have 100GB of stuff, your C drive might not be appropriate.
Because hydrus stores everything inside itself, it is entirely portable. You can extract it to a usb stick, move it from one place to another, have multiple installs for multiple purposes, wrap it all up inside a truecrypt volume, whatever you like. The .exe installer will write some unavoidable uninstall registry stuff to windows that'll mess with this, but the client itself will run fine in a different location.
updating
You don't have to update every week, but I generally recommend it. The different versions of client and server can talk with each other until I increment the private network protocol version (which happens every couple of months), at which point you will get polite error messages if you try to connect to a newer server with an older client or vice versa. Read my tumblr posts and judge for yourself what you want to do.
If the client you want to update is running, remember to close it first!
If you use the installer, just download the new installer and run it. It should detect where the last install was and overwrite everything automatically.
If you extract, then just extract right on top of your current install and overwrite manually. Then run client.exe as normal.
All your files and settings and synchronisation progress will be remembered after the update. Unless the update specifically disables something, nothing will be deleted or lost.
Whenever you start the client, it checks the version of its database. If the database is old, it makes the appropriate changes, in sequential order (i.e. to do v70->v75, the client would first apply v70->v71, then v71->v72 and so on), until the database is caught up. If this process will take a while (like an hour, sometimes!) I will say so in my tumblr post.
backing up
You do backup, right? Right?
I run a backup every week so that if my computer blows up, I'll at worst have lost a few days' work. Before I had a backup regime, I once lost an entire drive with tens of thousands of files, and it didn't feel great at all. I only push backups so hard so you might avoid what I felt. ;_;
I use ToDoList to remind me of my jobs for the day, including backup tasks, and FreeFileSync to actually mirror over to an external usb drive.
If you want to backup hydrus, you can either go database->create database backup or just shut the client down and copy the entire install directory somewhere.
I recommend you do it before you update, just in case there is a problem with my code that breaks your database. If that happens, please contact me, describing the problem, and revert to the functioning older version. I'll get on any problems like that immediately.
linux and os x
I now make OS X and Linux releases. They are not as good as the Windows releases because I am not as experienced in their OSs' weirdnesses. When I find time, I improve them.