My first Sheltie was extremely tiny and his ears were incorrigible! I tried every trick I came across - including fishing weights. When he was a year old, I gave up, and for the rest of his long, long life he had just about the cutest pricked ears every. And I wouldn't have changed them for anything - it gave him a particularly alert look, which suited him.
Bela came to me at 5 years old, and either her ears are those rare ones that tip naturally, or somewhere back in her past, someone spent a lot of time on tipping her ears. And tipped ears suit her perfectly, too. I love to watch her ear tips bounce as she trots around. It's just *squeeeeee* cute!
As long as you're not showing, the ear tipping is just a matter of taste. I showed my male Sheltie in obedience for a long time even with non-tipped ears. I would get a lot of flack ringside because of those ears (and some very snooty looks) until we got in the ring - he loved doing obedience and wagged his tail the entire time. I think we ended up getting more qualifying legs that we really deserved due to his perky, happy, smiling attitude. And those ears were priceless!