I started programming Assembler back in 94 or 95 using TASM (the Borland assembler, quite similar to the Microsoft's MASM). I was comfortable with that configuration. Later I began to embed code with the Borland C assembler, that was easy, but it was difficult to make some complex tasks... And then I had to switch to Linux... hummm, there were no Borland C nor TASM oh! What to do! Fortunately, gcc provided a much better C compiler (the Borland C was completely surpassed!) but it was hard for me to get used to the assembler included: GAS. It uses the AT&T mode for writing assembler... but it was hard!
For some time I didn't need assembler, so I forgot some of my skills about AT&T. However, when I started my Ph.D. one of my professors asked me to optimize some common algorithms using MMX. Thus I had to go back to the old days that I used AT&T assembler embedded in gcc. After that, I have made comparisons using both AT&T and Intel, and also Intel Intrinsics (a C library which allows to use assembler functions directly in C). I have found that gcc + AT&T is the fastest of the three options... so I have no doubts, I will use gcc + AT&T, rather than Intel C Compiler + Intel Assembler or Intel Intrinsics.

Have you found the same difficulties as me? Tell us your experiences...