With the announcement last week that Android 3.0 is for tablets only, do you really need a dual core Tegra 2 smartphone? In brief, the answer is not yet. GSM Arena recently posted a first look at the LG Optimus 2X which is powered by a dual-core 1GHz ARM Cortex-A9 proccessor, Ultra Low Power GeForce GPU, Tegra 2 chipset. Their conclusion is that the dual core Optimus 2X not really feel any faster than the current crop of single core 1GHz Android smartphones.
The reason behind this is the operating system. Neither Android 2.2 (Froyo) or Android 2.3 (Gingerbread) is not designed to run on dual core systems, and does not really make full use of the second processor. It does not mean that the second processor is wasted. The dual core architecture does allow for 1080p video playback and capture, whereas a single core smartphone is currently limited to 720p video playback and capture. For now, that is really the principal benefit.
Software is coming which will start taking advantage of the dual core processor. Games powered by the Unreal 3 gaming engine will start coming out for Android, we will probably see the dual core optimizations found in Android 3.0 (Honeycomb) start migrating its way to Android "2.4" be middle of this year.
If you really plan to make use the 1080p video recording capability, I guess you will want one as soon as possible. It is nice having the ability to playback 1080p video too, but I do not really see the advantage of having the ability to play 1920 x 1080 on a 800 x 480 screen as that big a deal. If you are a gamer than you will want one in a few months when new gaming titles taking advantage of the dual core processor start to come out.
For those who just plan to use the phone as a smartphone, you probably want to wait for at least Android 2.4 to come out, and even then difference probably would not be noticeable. While all this high tech is really interesting, for the remainder of 2011, mundane things like larger batteries or more energy efficient components would be more practical and useful improvements.