Lasik/wavefront/etc. works by ablating (destroying) layers of the cornea. The cornea is only so thick. Long-term effects of a thinner, weaker cornea are relatively unknown. Since the surgery isn't brand new, there don't appear to be serious medium-term complications. But particularly with repeated "corrections", this is an issue. At some point, the cornea may get thin enough that doctors won't be willing do any more corrections.
Most complications occur due to insufficient diameter capability of the laser system. The surgery will create two curve types on the retina. The area ablated will have the proper curve to focus light accurately on the retina (back of the eye). The surrounding area will have the original curvature. Imagine a sphere. now imagine drawing a small circle on the surface and flattening it so that it has the curvature of a larger sphere. Note that there will be a non-continuous curvature change between the ablated portion and the surrounding portion.
Now, if you've ever even looked through glasses, you know that, if you're nearsighted, there's some duplicated sight area... if you can see something through the top or bottom edge of the glasses, you can probably also see it right above or below the glasses. Same effect with the sudden curvature change of the cornea, except the cornea modification results in circular effects like that. They show up, obviously, when the pupil dialates beyond the ablated area. The two curvatures focus the same images differently on the cornea, resulting in radial ghosting.
Bottom line: make sure, if you value low-light vision at all, that you know how much your eyes dialate (in mm/cm). Make sure the surgery ablates at least that much.
The other issues are primarily the result of infections, or improper replacement of the corneal epithelium after it's sliced away to do the laser ablation. If _anything_ feels out of the ordinary right after it's placed back, notify the doctor and don't go anywhere until they check it. If you wait a day or two, healing/scaring/ridges can occur, and this is very difficult to fix, pretty much beyond today's standard LASIK doctor's capabilities.
Read up on it as much as possible. If you have relatively thick corneas and you know the ablation area will cover your dilated pupil, the most important thing is to be able to recognize bad flap replacement and bring it to the attention of the doctor in a way that will get his/her attention.
What will be really interesting is when doctors manage to grow corneal cells and transplant them onto existing corneas. Then thickness will not be an issue, nor will most of the other problems. If they screwed up too badly, they could transplant a thick corneal layer and do wavefront, provided they could avoid internal optic problems between the layers, or fill in problem areas (pits/grooves/whatever) with externally-grown corneal cells before adding the new layers.
