There are currently 8,256 nodes on the network, you can check in the node UI if you have a registered node (just go to registered nodes IP address and use wallet address as password).

The current time to a reward is 8256 nodes / 48 rewards/day = ~172 days (5.7 months)

With a reward size of 1500 TNT, the current 8256 nodes, and a minimum balance of 5000 TNT, the yearly ROI (in TNT) is ~63.7 %.

The dollar amount ROI is a little more tricky and dynamic to calculate as it is a function of the number of nodes on the network, future reward amount / reward frequency, and VPS hosting costs.

 On the short term, I think it is easiest to look at it as a 30% ROI in TNT in ~6 months for $30 in hosting costs ($5 x 6 months). Basically if you are a long term holder and believe in the project and higher future token prices, its not a bad idea to run some nodes. If you are looking for a month to month stream of income, at this point the risk would outweigh the benefits with such a long time to reward and price volitility over that time period.... but this mentality applies across the board for crypto mining in general. Historically there have only been a few 3-6 month windows where mining is extremely profitable; in between booms, you're lucky if you can break even.