These are just oddities that don't really fit anywhere else at the moment. Please feel free to contribute if necessary.
Floating point emulation is now done automatically in the build process. Just use floats and doubles as you would normally, and support for them will be compiled into your .lx files. Be aware that floating point math will take about 50% longer than integer math that has the same results.
random() and srandom(int x) are now available in legOS. To use them, just call srandom(int x) at some point during your program startup. x is a "seed", which allows you to get the same sequence of numbers if you so desire (by passing the same seed) or to generate more truly "random" numbers by feeding in, for example, LIGHT_1. Be aware: unlike the "standard" implementation of these two functions, there is no "default" seed, so if you don't call srandom() at least once, random() will return the same number over and over again.
ints and such may be slightly smaller than you are used to in "real" programming. In specific, an int is only 16 bits long, so it will overflow at around 32K if signed and around 64K if unsigned.
Not that this means much until you've actually compiled code, but there is 32K available for the entire system. The standard OS configuration should consume about 18K of that, and judicious use of config.h can reduce this to 14K or so.
If you need to ensure that LegOS has a particularly small memory footprint, you can edit the #defines in the boot/config.h file to prevent the compilation of certain features. The features that can be turned on and off include:
if you aren't using threads: task management, semaphores, and memory management
IR communication with the computer
rotation sensors only