It's a tough call, gift cards are great to get, but I feel kind of cheesy giving them.
If you have a friend or family member who's really into say, golf, and you want to get them something golf related, you're automatically in over your head, and will probably get them something too basic for their hobby, or something they already have. However, if they have one of those big golf superstores in thier area, getting them a gift card allows them to grab whatever they want, so it's a good gift.
Likewise, if you know someone wants an MP3 player, or something like that, but you don't know what kind, where they want to get it, what features matter to them, etc., a gift card with a note saying something like "for that MP3 player you wanted" is good gift.
The only problem is that they're kind of impersonal. Perhaps a gift card plus something that's maybe inexpensive, but a bit more thoughtful, so they know you tried.
For a spouse or sig. other, gift cards prob. won't cut it.