Guys, guys, guys, why such extreme positions?!?! This has been covered extensively before but there are definite and perfectly valid pros and cons to EACH form of travel and what is right for one person with their own particular circumstances and preferences may not be right for someone else. Incidentally, PT, I didn't check latinman's link but I'm sure that means the those tourist vans leave twice a day at 8AM and 3PM for the 2.5 hour trip and NOT that it takes 7 hours. C'mon now I could probably bike it faster than that. Also Sandinistas point is a perfectly fair one. For many of us it is not worth spending $125 for 2 people by car vs. taking at most 1/2 hour longer each way and paying less than $20 for 2 round trip fares, when we could be spending the difference on 4 MP sessions at Oasis instead or even putting the extra $100 into our GFE's pocket which she is bound to appreciate a hell of a lot more than the cab ride.
The obvious pro for a private driver is that one can leave whenever they want and get door to door service. The obvious con is that it costs significantly more. Some of the other alleged negatives for the bus, that PT seems have something against, aren't really major factors. The public buses that I have been on all have been reasonably comfortable (certainly not smelly), but certainly not radically less comfortable than the cramped back seat of the typical cab with worn shocks. Sure, with a private driver you can stop whenever you tell him to. I usually make it a point to go to the can before any long ride no matter what type of vehicle I take and going 2.5 hours without a pit stop has never been a problem for me. Longer bus trips usually include stop along the way. As for the duration of the trip, if you take the express bus it won't take much longer if at all than what it takes in a private car. If you can get to Jaco in much less than 2.5 hours in cab then either there is esceptionally little traffic or the cabbie is making passes that I just as soon prefer he not attempt.
The big advantages for taking a bus are obviously the cost ($2.11/pp from SJ to Jaco vs. $50+ to be split by however many you can comfortably fit in the car) and as even PT has pointed out the opportunity to meet real Ticos. On my last bus trip to Sta Elena I had a great conversation with a Tico (me practicing my broken spanish and him practicing his english) on topics ranging from soccer to the differing attitudes of Ticos and Gringos towards Bush and current US foreign policy. The big negatives are a) that you have to go to the appropriate bus station (rather than get picked up) b) wait amongst the exhaust fumes for your bus to leave and c) the buses leave according to their schedule not yours and then only a few times a day. The express bus to Jaco leaves SJ from the Coca Cola bus terminal 3 times a day at 7:30, 10:30, 15:30 and returns at 5:00, 11:00, 15:00. If you're traveling with a chica, good luck getting her to show up on time.
The option that Latinman was referring to is actually a tourist van. It is something of a mid-priced option. It is arguably more comfortable than the bus and they provide hotel pick-up and drop off (which adds to the travel time if many hotels are involved). OTOH, it is still limited to scheduled departure times just like the bus. As latinman suggested, this is really only a practical alternative if you're traveling solo. The price is $21 per PERSON, which is only much less than a private driver if you're paying only one fare or don't have anyone to split the cost of the private car with.
Bottom line, if you're traveling solo, as carepilot might wind up doing, and/or can be flexible as to departure times the bus is definitely a highly economical alternative. If you're traveling solo but think the bus will not be comfortable enough it may be worthwhile to pay a little extra for a tourist van. OTOH, a private driver may be a more desirable alternative if you have someone to split the costs with or would have to cover the fare of an accompanying chica anyway (ie reducing the cost differential) either of which would reduce the added cost of a driver to a point much closer to one's personal financial comfort zone. Another valid justification for choosing a driver is if the ability to leave, stop and go whenever you want are of paramount importance and you don't mind paying the premium for that advantage or you have a tight schedule that simply doesn't mesh with that of the public bus.
To use PT's case as an example, if you're planning a day trip to manuel antonio, can't get your chica down to the bus station for the 6AM departure, the next express leaves at noon meaning you'd have to leave only 1.5 hours after you got there if you wanted to catch the last bus back. Of course even if you took a private car, you would be spending as much time driving as you would at your destination, which makes the whole idea seem impractical to me anyway.
For those interested in PUBLIC bus travel here is one of several sites that provide a complete list of schedules, fares, etc.
http://www.costaricareisen.com/info/busse_eng.htm