Cubase to Logic
For what it is worth, I have successfully brought C5 songs that included MIDI data into Logic 8 via OMF without any problems, after firstly opening and saving them in SX3. However, from memory, I think I had problems trying to open songs created in C4 as SX3 would not recognize...
Move to Logic 8 from Cubase SX3
Just to throw in my two bob's worth... Jumping from Cubase SX3 to Logic 8 was the best thing I ever did in terms of music production and general software sanity. I felt right at home from the beginning, and though there were a couple of ways of doing or accessing...
I also have made the recent jump from Cubase to Logic, and am loving it, even though Logic does the same things as Cubase but in what at first seem to be weirdly different ways. Stick with it, and I am sure you will come to love it also.