My '09 mac pro just became my main computer so I need it to access my iCloud account. I don't want to break anything so I'm a bit leery about upgrading the OS and wondering if I should go all the way to ML or go with Lion (which was running nicely on my Macbook until the boot partition got corrupted). If I go with Lion the nice thing is I'll eventually be running one OS on both computers. Are there likely to be problems if I go to ML or Lion, and which would be safer? I'm running only pretty standard applications/devices (PS CS6, Extensis Portfolio 8.5, Bridge, Lightroom, Canon EOS stuff, older Wacom Intuos tablet, HP Laserjet wireless network multifunction printer, Script Debugger, various well known utilities) so I'm not too worried about those but I do have a SATA 3 card and external enclosure from Sans Digital. Should upgrading be fairly uneventful and should I go Lion or ML to ease the process? For mail I do need iCloud and I don't have time right now to solve incompatibility problems. Insights, experiences appreciated.