The thing I am wondering is the difference between a quad core (I have a dual core at present) and a dual core really that noticeable? I know when I went from single core to dual the difference was very noticeable. Also the 720QM has hyper-threading so that means it would actually have 8 logical cores.
Well it will depending on a few things:
First how fast was your old laptop.
Second it really depends on what your doing (games, web surfing, ect)
I cant say if you'll notice a difference between your old laptop and this laptop but depending on what you're doing it can. Video editing is a big plus with a core i7 certainly with HT if it can be used by the program. gaming, turbo boost will probably make things better.
Now 1 thing i can say is, with turbo boost, this cpu can be a 1.6 ghz quad core cpu, 2.4 ghz dual core cpu, or 2.8 ghz single core cpu. So in theory if your old laptop has slower than 2.4 GHz then you maybe able to see a the difference.