Do you do anything to your cards so that people know you hand-made them? If you don't, you definitely should. My family tried to convince me of this for a long time but I saw personalized stamps as a waste of $ that I could spend on something else. Well finally about 6 months ago, I bought one.
Let me tell you, it was the best decision. I wish I had listened sooner. For such a reasonable price, it makes your cards look so professional. Let's be realistic too - how is it a waste of money when it costs $12.95 - $24.95 (depending on what you want it to say) and you will use it on EVERY card you make? It would make an excellent gift for any crafter on your list because it is the gift that most crafters won't buy for themself!
I love mine! Come May, I'll be ordering a new one since I will no longer be Allison Frandle but rather will be Allison Bertamini!
I personally use the one pictured ($22.95) and when I make non-SU cards, I just don't stamp the copyright portion of the stamp!