Dear friends,
I am a computational physicist, but not much into hardware of laptop verymuch.
I am about to buy a laotop where i can develop my codes(which are preety cpu demanding, so I am looking for i7core).
Now, just before i set up my mind for Dell xps15, I saw another from dell xps 15z(http://www.dell.com/us/p/xps-15z/pd.aspx
Now, this is much new and not yet quite reviewed.
I can see both of them have similar specs like intel i7 proc and upto 8GB RAM. What else I should look for(do decide if its a real workhorse?)?
Plz suggest.

The laptop you linked (dell XPS 15z) has nVidia optimus, which is not supported with linux. Most optimus laptops cant use the nVidia GPU, and if you dont do some mods to the OS the nVidia GPU just sits there, eating power and creating heat.

It is possible for optimus laptops to work with linux, using the nVidia GPU, but you need a hacked EDID file, or a BIOS switch to force the nVidia GPU.

so you are best off avoiding any laptop that use optimus.

XPS 15z also only has a dual core i7. If you really want a lapop with a lot of CPU power, the quad core i7 laptops are what you should be looking at. Mind you, the good laptops with a quad core i7 would be just as much as a netbook and a desktop with a quad core i7, or a quad/hexa core AMD phenom II. The desktop would have a fair amount more CPU power than the laptop.

Actually , the machine I am looking at(in India)is http://www.dell.com/in/p/xps-15z/pd?...s-15z#TechSpec
It says, NVIDIA GEForce...no mention of optimus. So I guess its w/o optimus.
Will linux(specially fedora) be able to use the most of it?

Its got optimus. Its the same model as the US XPS 15z-

http://www.dell.com/us/p/xps-15z/pd.aspx

Optimus technology is not yet supported under linux, so you better avoid it. In any case, you can always disable the nvidia graphics card as explained here
http://ubuntuforums.org/showthread.php?t=1713308
and here
http://forums.fedoraforum.org/showthread.php?t=266620
The question is: would you pay for something you will not use? Well, if you have a double booting (Win, Linux) you can always use the nvidia card under windows, given that you don't need a dedicated gpu for your purposes when using linux.

Best
G.