I've got a divorced couple working in my office.
Not sure if they met here or were already together when the started working here (They have children and were already divorced when I started here). I hear that there was some animosity, but they both continue to work here (although their offices are on separate floors...probably by choice).
I had a bit of a thing with a girl who started a year after I did. It was never more than some occasional intoxicated lovemaking, but I think she wanted more and was upset when I started dating someone for real and cut it off. I didn't find it to be too awkward although she might have (and there was a happy hour or two after the fact where she was upset). I did get eventually get promoted and she ended up being one of the people who did the most work for me--I thought things were fine...she did good work although sometimes I felt a little weird bossing her around (although she wasn't the only person I felt weird bossing around since I was new to bossing people around and my underlings were my former peers). She left the firm to go back to school a little while ago so I suppose the issue has fully resolved itself.
I think it's not so bad in an entry-level environment...especially in a larger firm or in industries where you aren't expected to stick around. If most people are only there for a couple of years before going back to school or moving on/up, it really won't matter much if something does end poorly (although by now, you should probably know whether you are the kind of person who leaves things in an awkward mess or not). My ex worked for a big company right out of college in a division that hires a ton of analysts. You end up with this situation where there are new classes of analysts coming in every year, all moving to a new mid-sized town where most of the locals probably grew up there and have tight friend groups...She seemed to have a ton of friends who found marriage or long term relationships among coworkers (or possibly clients), and lots more friends who spent time hooking up with fellow employees. Nobody works there anymore (all having switched jobs or transferred to other positions in other offices), so it's not like the failed relationships had any lasting impact.