yes it is, but you typically have to get a new motherboard and cpu at the same time because of new socket standards.
i like upgrading over time. i started out with an i5-2500k, a gigabyte atx board, a gtx 460, cooler master case, 1tb hard drive. since then i swapped the i5-2500k and gigabyte into another computer, got 2 new cases one for the old system and a new itx case, got an itx mobo, an i5-3570k, got 2 ssd, got 2 different heat sinks, a gtx 480 which i replaced with a 670, a 2tb hard drive
i kept a lot of my stuff around and ended up making 2 high end computers out of new parts and my old computer. i am BIG on upgrading. you can sell old parts to fund new parts or keep them around and eventually build another computer or 2. the more you know about technology the more you will want to upgrade. i think i have consistently upgraded something every 2-3 months thats anywere from a new mouse or keyboard to a new monitor or graphics card upgrade