Apple Lossless or not?

I am new to this website and somewhat late to the music server discussion.
I recently began running a spare Dell desktop as a music server using iTunes.  It feeds a Cambridge Audio DacMagic via USB and then into my system.  I am listening and enjoying digital music now much more than before I began using the computer and the DAC. 
 
The question I have is this:  I only rip CDs now using the Apple Lossless format, but much of my music previously ripped into iTunes is in mpeg or AAC formats.  iTunes provides an option to convert all that music to Apple Lossless, but will the resulting music file duplicate the CD music file bit for bit as if it had originally been ripped from the CD in the Apple Lossless format?  It seems reasonable to me that there would be some degradation through the conversion.  If so, please explain.
 
Finally, I've been reading that many are somewhat disparaging about iTunes and Apple Lossless format.  What's wrong with it?

Carl Espy
c [dot] espy [at] live [dot] com