What lead me to check out Sythe was the market, it was and is the biggest market for the game that I seeked to do business in (Runescape). After I had done some trades and gained a bit of reputation I decided I wanted to start an actual small business, so I did and opened my own Questing Service. What suprised me was the amount of people that immediately trusted me enough to let me do quests on their account, my little business grew at such a high rate that I was full of orders most of the time.
Besides the market related stuff that had drawn me to Sythe, the active userbase and the events that are hold every now in then (in which you can win awesome stuff) is what kept me using Sythe. An example of a few subforums that I especially liked are the dicing competition subforum (in which you can win free stuff by simply posting in a thread), the spam subforum (in which you can post almost whatever you like) and the Runescape related subforums. In regards to the dicing competition subforum I was lucky enough to win about 150M in RS3 gold, which is equivalent to 35$.