I just bought a DS and yes it was worth it! So far I'm very impressed, I got New Super Mario Bros with it and its great fun. Even my none-game playing family love it.
At first I kinda regretted blowing £120. Then when I got home it didn't really matter that it cost so much, it was money well spent in my honest opinion. I was never really into handhelds but this totally changed my mind about them. It even got me playing old GBA games again 
Now I have to start saving for a xbox 360 all over again...