I have a 2009 iMac with 4G RAM. According to spec, that is sufficient for Lion. However, I am a bit concerned about how much the OS actually uses. Does anyone have this hardware with Photoshop CS5 and, if so, does CS5 operate OK?
There are people using the entire CS5 suite in 4 GBs of RAM. It's slow going but it works. PS should be fine by itself. Keep an eye on your RAM usage with Activity Monitor which should help you determine if RAM is getting tight.