For the bytecode caching:
The Bytecode caching (which i considred, beside security issues like injecting code in create_function), as mentioned above, can be practicaly ignored.

Because that performance+ what bytecode caching brings (for that ~400 lines of code... ähh $strings to be bytecoded :-) ) is not more than 0.01 sec.
This 0.01 sec. is almost done in the first rounds of any cipher of using inlinecrypt. So the missing bytecodecaching speedup is, imho, ignoreable.


For memory issue:
We/i was considerd, discuss (3 monts ago) and testing it. 

create_function(), of course, is using permanent memory and there is no way of release it.

For each cipher, process wide, it would be max. 5 function. For each $mode one... process wide (using static class var holding the function name). 
Exception is Rijndael. the max amount of function creating by create_function is ~50... process wide... of course.

In my tests that time (Linux/32bit/php5) using all ciphers, all $modes, all $block_length, all $key-lenght costs additional ~20MB.
Its possible to reduce it (using if()'s in the function code) of the cost of perofmance to ~5MB (estimated)

However... create_function() will in no case called endless. Independet of the $keys, $modes, $block_size and amount of Crypt_* objects one is using. 
The design of the inline crypt implementation ensures that.
So there is, of course, a memory usage which can not bee freed, but there is no memory leak of endless growing memory.