There are some great online tools to take your custom text and “heart-ify” it. For starters, the following 3 sites make word clouds in the shape of a heart:
Festisite flows text into a spiral heart
Scrapcoloring lets you type in short text and then fill it with a heart pattern you can also customize. You can also generate high resolution background paper in various heart patterns.
Says-It generates circular text and a heart border.
And the software you already may have also has some cool text tricks for you to try. If you want to flow paragraph text into a heart shape, for instance, it is quick and easy to do in Inkscape. My one minute video is here. (Instructions for doing this in MSWord, PowerPoint, etc. are here, but I had little success with them.)
You can also flow text around the outline of a heart using Text>Put Text on Path in Inkscape or in SureCutsALot with the steps shown in this text on path video. Studio with the steps shown in this video. Make the Cut also has this capability.
And one more, custom candy hearts, classic, if too low rez to be very useful
Have fun and Happy Valentines Day!
1/14 update: This post was made before my Silhouette days, but I want to add this link for the Silh crowd.