I use it and I find it far more convenient than the tickets/cash I was using for a variety of reasons...
First I don't have to carry around the tickets any more - which means no more forgeting the tickets in my other jacket or other b.s. like that. I always have the card in my wallet.
I also like it because I only get charged the exact amount of the fare. I no longer lose the quarter in non-peak hours. Not a huge deal, but still.
I can add money to it outside of metro station customer service business hours.
Transfer tickets are no longer needed. The card tracks my time won't charge me if I'm still within the alloted time.
It can be used ferries, trains, etc. as well. So that's kind of cool.
The only reason I wouldn't get the orca card is if I only road the bus and I road the bus everyday - weekends included. Then I would get an actual pass. But you have to ride it everyday, more than once a day for the pass to make financial sense. I think you need to take around 36 seperate 2.50 trips a month for a monthly pass to start working in your favor.