Are buttock implants comfortable when sitting for LONG periods of time (e.g., plane flights, long drives, etc.)?

Your are indeed correct in that we sit at a lower place than where the implants are positioned. You are also correct in that some people slouch when sitting and therefore may apply more pressure to the implant. However it has been my experience, after 13 years of doing buttock implants, that by around 5 - 6 months after surgery the implants more or less become "self". Meaning that the patient's body kind of grows accustom to the implant such that it feels a natural part of the body. The same is often true for breast implants as well. Glad to help. 

   The implants will take several months before they will feel more comfortable.  The plane of placement and size of the implant will be factors as well.Kenneth Hughes, MDLos Angeles, CA

If done right they will be comfortable. There are different operation options such as implant shape, implant thickness, implant cohesion, placement over or under the muscle etc.This is a great operation for the right person.