That depends on the mark and the use. If it's famous there is more broad protection of potential confusion (i.e. saying traveldisney is a whole lot different than saying traveldrink). If there's conflicting businesses interests then infringement is very possible even if you don't have a class overlap. What you really have to ask yourself is how unique is this word, how similar are your network sites going to be to their business and where might they feasibly expand to in the future. If you're uncertain a trademark attorney can certainly help, or you can simply decide to chose another name.