I *could not* get it to work via display:inline. It was literally driving me nuts. The div code rendered fine on FF 3.5, but broke on 3 and IE as usual, sucked. The only happiness for IE, FF, Safari was to use <span>. I ended up modifying the plugin (which I wanted to avoid!) but alas, my sanity couldn't find the combo that would work.
To sum up my experience without showing screen shots, I have a single line that has text that's float: left, and sociable float: right. When in a <div> for whatever reason, IE and FF 3 would render the <div> slightly lower and the line wasn't straight with the text on the left (even with display:inline which I tried), again it looked fine in safari and FF 3.5 and IE 8 (I think).
The only way all of my tested browsers worked was by using <span> for both left and right sides of the line. Very annoying! I hate hacking plugins to make this work, but I like the was sociable displays a neat, small tidy row and so I was determined to fix it.
So personally, I think it would be a piece of cake to add a toggle to the preferences panel that simply told sociable to use <div> or <span>. I know I'd appreciate it!
If you guys have any ideas why I might have had these problems, I'd love to hear them.