I've read online some people being dissappointed with ds games on the 3ds but after lots of examination between different games I cannot tell enough of a difference either way to matter. If you get a 3ds I gurantee you will be happy playing your ds games on it.
3/28/2013 UPDATE: Today marks the 2nd anniversary of me owning my 3ds and I can easily say it's probably the best overall gaming system on the market with such a huge library of awesome games. My mom picked me up a pikachu 3ds XL this morning so now I have to decide if I'm going to continue playing on this or switch my stuff over to the XL. Since this video I have sold my ds lite as well as my dsi XL hopefully the new owners are enjoying them. One more thing feel free to add me as a friend on 3ds I love a good mario kart battle here is my friend code 4382-1994-1871.