you don't want someone to build it for you? *tear*
this build actually isn't that bad, all in all - an i7-870 is what i'm looking at when i upgrade, and the amount of ram isn't bad, and the gfx card isn't bad. you're paying a premium for the "support" that dell offers, however - particularly since dell's support is easily the worst in the business by a large margin.
the biggest issue about big-box builders is simply what they don't tell you. what kind of hard drive is in there? it's not a western digital caviar black, not at that price, and that means that the mean time before failure (MTBF) and warranty is likely under three years - possibly even one, if it's a spinpoint or seagate xt. what kind of motherboard? it's not a gigabyte, asus, or evga, or even a biostar or asrock, and that means that your system is going to pull more power thanks to crappy capacitors, run slower thanks to poor connectivity between the main bridge components, and be less stable due to low-quality build materials. what power supply is it? what efficiency? it's not a silverstone, antec, seasonic, corsair, or ocz psu, which means it's probably not japanese caps, probably doesn't have proper cooling on the system, and probably has a MTBF under three years. it likely has a low efficiency, too - lower efficiency costs more in the long run to run - by a lot - as well as increasing the heat in your case due to waste energy, reducing the life of your psu, and feeding your system power that's less regulated with more ripple and distortion than in other systems. what kind of ram is that? it's likely cut-rate kingston, with no heat spreader and random timings, meaning that it's not as stable, it'll die much faster (i've had kingston chips die in six months before on a load-bearing machine), and since memory relies on having matched sets to get good performance and stability, you won't be able to replace it and get dual or quad channel, either.
that case has virtually no cooling, too, meaning that your -870 - a chip that requires 95w of heat to be shipped off chip, if i remember correctly - will have little to no reinforcement for the stock cooling it has. this'll result in higher temperatures, reduced longevity, and shorter times of load before a bluescreen or reduced efficiency.
...shall i keep going? at least contact me for an estimate, man =) i bet i can soothe your worries in no time flat. if nothing else, i can help you figure out what you need for your build. the above pick seems kind of random - are you doing gaming, or music, or a little of both, or what? it's kind of an all-around pick - you could get a lot better deals by focusing on what you want, i think.