i have minolta xt and siemens sl45i. When mmc on my minolta is full I just put the mmc I use in sl45 and there is no need for formating, pictures are saved in their own folder. I'm planing to buy sx1 so i was wondering (sx is much more complicated than sl45) if I would need to format my mmc when moving from one gadget to another?

No need to format the MMC for the SX1 (they should be using the same MS-DOS -originated FAT file system; the SX1 is, at least, but to my experience all memory cards for all digital cameras I've used have, too).