Well, it works ;P. It is still "in flux": core language features are changing every few hours. However, it has already changed the workflow of the "elite" iPhone developers that write most of the extensions you see in Cydia: having a language that changes doesn't matter when you are mostly using it at the immediate console. I'm hoping, however, that I manage tolock it into something that feels "correct" in the very near future.
I pronounce it "sscript" (with a geminate, aka long, 's'). I doubt anyone else will pronounce it like this, but I have my hopes.
Right now you can find releases of it at: http://www.cycript.org/debs/. This package depends on MobileSubstrate and libffi (both of which are in Cydia). Note that Cycript is an open source project, with its source code available at: git://git.saurik.com/cycript.git. There is an IRC channel at irc.saurik.com, #cycript.
Although you can write full applications in Cycript, the fastest way to get playing with it is via the immediate console: just type "cycript".
Structures are also supported (although unions are currently on the todo list and bitfields are still DOA): they are bridged back/forth as much as possible. You can specify them using either array syntax or in the form of dictionaries.
Access, allocation, and casting of pointers is possible through the usage of the Pointer and Type classes. Pointers can be indirected using the * and -> operators, as in C.
Objective-C @properties (some of which are auto-detected, as Apple doesn't always compile them into the resulting binaries) can be accessed using . notation. Currently, auto-detected @properties are usable, but aren't enumerable. This namespace is strictly separated from that of instance variables, which you can access by indirecting the object using * or ->.
Fully-fledged Objective-C classes can also be declared using @implementation, which also takes on functionality of Objective-C's @interface. Right now, declaring instance variables are not supported, but will be in a future version: for now you must provide an empty variable block.
The @implementation syntax can also be used to extend existing classes in the form of an Objective-C category. Note that type signatures, however, are not yet supported, so you end up heavily restricted in what you can add via this mechanism. In this case, one can also use a parenthesized expression as the class name.
Cycript is also capable of accessing normal C functions and variables. Knowledge of the type signatures of various functions are provided in the bridge definition file, which is currently a plist stored at /usr/lib/libcycript.plist.
Cycript attempts to do its best to serialize information to the console about objects. In particular, CoreFoundaton objects bridged to Objective-C are detected and printed using CFCopyDescription.
This isn't quite "ready for primetime", but you can download the example HelloCycript.app from http://www.cycript.org/examples/ and put it in /Applicatons.
Probably the awesomest thing you can do with Cycript is to hook into an existing process using the -p argument to the console interpreter. As an example, let's hook our way into SpringBoard and start spelunking.