@soiramk, I don't know anything about Steam cloud support for saved games, but your question got me searching for answers...
The saved game file for Machinarium is called a .sol - so "machinarium.sol" is the file that holds all your saved games. Look for it on your system; it's TINY, measured in tens of KBs. And, from what I've been reading online, the saved games of such titles as Fallout have save files as large as 9 megs! So it technically wouldn't break the bank for Steam to support Machinarium.sol saved game files. Maybe you could ask the people at "Steam" how this could be done?
Or...
You could read through our "
Shared Machinarium .sol Files" Thread and figure out for yourself how to transfer your saved games from MAC to PC and back again (and forget all that cloudy Steam stuff)
Let us know which route you take and how things work out.