Scott... it depends on what you want to get out of it as to whether it's worth it or not.
For me, the track accuracy trumps all, and that alone is worth the price of admission and track add-ons. You definitely won't get the eye candy that you find in Forza or GT5, but that's because that processing power is used for physics.
You can choose to race in iRacing official sessions (Race, Qualifying, Time Trials, or Practice) or in hosted sessions (some are open, some are private.) Your Safety Rating (the rating used to determine your license level) is NOT affected during a Practice session, or in league sessions. The Safety Rating (known as "SR") is a major difference between iRacing and every other sim out there. It's intent is to basically simulate damage to vehicles over time, a "barometer" of a driver's overall safety and fairness... both of which serve as a deterrent to over-aggressive "normal" online racing. It's not perfect, but I think it does it's job well (some don't though, but no one has come up with anything better.)
I'm not on it nearly as much as I'd like to be. Right now, I'm participating in a league called "FSR - Friendly Slow Racing"
http://flyingkiwi.org/iracing/ ... I'm running the "SIMR" series that races every Sunday starting at noon. Some races are Daytona Prototypes & Mustangs, other races are Radicals, Miatas, & Late Model stock cars, still others are Corvettes on Ovals (!)... all within this one series. It is an endurance series, so each race is usually 50 to 90 minutes long. But the point of the league is friendly, courteous racing (the slow part simply means anyone is welcome, even if you're slow.) It's an atmosphere much like our normal track days... everyone there is there to have fun and help everyone else. There is a point system set up for it, but no one really cares about it LOL.
So yeah... I'm a fanboy, what can I say
