Out of Memory

For most of 2010, my poor, almost five-year-old mac has been limping along.  It seemed to give me that dreaded "Your start up disk is out of memory." message more and more frequently.  It always strikes fear in my heart...Will I loose something or everything? What do I delete?  Will I delete something I need?  I have gotten into the habit of storing most of my documents on my iDisk...easy enough.  But, honestly, those documents were not really an issue in the grand scheme of things...the real culprits were all those photos.  Yikes! over 5000.  So, I finally invested in a little passbook external hard drive, and transferred all those photos to their new happy home.  Now I have like 49 G of memory.  I feel much better about that.