My SO is a PhD student in engineering; we met while we were both undergrads and have since both gotten masters degrees in engineering and psych respectively. I'm not currently in school (hoping that will change come september!!), but I live in graduate family housing on campus with him, so everyone in the entire apartment building is grad student either married or in a serious long term relationship (or someone in a relationship with a grad student), and a few of them (*gasp*) have small children. Most people seem to be doing okay.
I think being in a relationship definitely can and does in many cases work while in grad school. I actually think it works better if you're both grad students or have been through grad school, because then both sides are a little more understanding about the time and effort involved. At the same time, it kind of forces you to have some 'self-care' and engage in other activities besides school.
And about putting dating off...if you want a research career, you'll always be busy. If you dont, you'll probably always be busy anyway. you might as well learn to balance work and your personal life now.