One more suggestion, which I'm not sure is possible, but which would be swell to have:
When you use set mark (ctrl-spc) and select a region downwards, then use shift-meta-L to split into lines, the line with the mark retains its region when you move the cursor around. So if you want to, say, add a comma to every line by hitting C-e comma, the entire first line will be replaced with a comma.
Alternatively, if you set a mark and create a region upwards, split into lines, then hit C-a or C-e, the multiple selection disappears entirely and only the marked line has a cursor.
Maybe you could, I dunno, remove the mark in that case? Not entirely sure what is to be done.
One more weirdness with marks: set a mark near the end of a file, then hit alt-shift-> to go to end of buffer. Now type C-n and C-p (or up and down arrow) and note that the cursor can no longer move past the marked line.