Shuttle Express can be a good alternative to a taxi, depending on how far away you live from the airport. You do have to wait a really long time, usually, at the airport when you are heading home, as they like to fill the vans before sending them off. This can be INCREDIBLY annoying and frustrating when you just want to get home because it's late and your flight was awful. I've definitely bailed out on the Shuttle Express line to take a taxi out of sheer frustration and after having waited over an hour.
Taking the van TO the airport is much nicer because you can wait at home for the Shuttle Express to come and get you. The only problem with this is that they pick you up WAY TOO early - like several hours before your flight leaves. I guess this is because they guarantee that you won't miss your flight, but when you have an early morning flight, I'd almost rather miss it than get to the airport 2.5 hours early!
Overall, I've stopped taking the Shuttle Express because it's a waste of time. At this point I'd rather pay the money (not all that much more) for a cab, or take the bus if I have time to spare since it's about $30 cheaper!