Trying to decide between an attached spa/hot tub, or a portable type.

[waterbear]

Waterbear,
Is the air blower and bubblers two seperate items? Could you tell me how they operate? One pool contractor discouraged me against the injection of air, stating it was introducing cold air into the hot water. Is there any validity to that statement?
As I understand, on a basic spa, it's high pressure, hot water, that is being injected into the spa.

If all you have on a 'basic spa' is hot water coming in it's not much of a spa, IMHO. Just check out portables and see how much water action they have. This is true of a built in spa or a portable. If you depend on only the pump to supply the water action you will end up with a very large HP pump which is going to be overkill for the pool in a shared system. Even using a variable speed pump, while a solution, is not the best in many cases.
If the ambient tempterature is cold then air blowers AND passive venturi jets (which are the type of jets used in spas) will lower the temperature of the water a bit. If your heater can keep up and is not undersized then it's a moot point (and when you consider that such venturi jets with air controls and blowers are standard on portable units and it is not seen as a disadvantage then I am not sure what your builder is afraid of, unless the heater he is proposing is not up to the job). If you are going with a spillover type of spa then it will basically stay at pool temperature and will have to be heated before use so you will need a heater with fast recovery time on the spa. However, venturi jets are standard spa jets and allow the air to mix with the water to increase the water pressure (and usually have a control to adjust the amount of air that is injected). Blowers add an additional level on top of this and might be hooked into the venturis or just plumbed to bubblers (air injectors). If your builder is not planning on using spa jets but only regular returns you will not have much water movement in the spa and, IMHO, it will be more of a 'kiddie pool" than a spa. Bubblers are air injector jets. Venturi jets mix water and air for more pressure and can be passive (uisng the motion of the water to suck in the air) or connected to the blower for even more pressure from the jet.