I need to do that too! Too bad the DS is so hard on my eyes or I'd play it more.
Time-travel: my son used to do and I'd whine about the weeds, until I discovered Wisp'll clean 'em up for you. Now I use TT all the time to hit up anything I've missed, like turnip sales or holidays. I don't know if there's a Wisp in the DS version.
My son and I play the GC version together all the time: we have three towns on memory cards and we travel between them. We exchange furniture and fruit and visit the island where we have our joint cabana. It's a lot of fun! We'll waste away an afternoon playing back and forth. He loves it because he's such a gamer and this is the one game I play
with him.
