When working with clients, I use MS Word or NotePad to keep lists of the MLS numbers we have looked at or are interested in.
To organize the lists, I put a short description at the beginning of each line. The MLS numbers follow, separated by commas. Like this:
Jan 12 looked at: 98280903, 98277414, 98281328
Jan 22 preparation: 98283878, 98280321, 98284890, 98259765
From there it is a simple matter to display the listings on Google Earth. I "copy" a row of MLS Numbers into the clipboard and "paste" it into the MLS Number(s) field on the Earth Point home page.
Download to Google Earth, and there are the listings. I can even take my laptop on tour and use Google Earth to navigate from house to house. Of course, someone else has to drive!