From the last thread:

Quote Originally Posted by jseah
Seriously?

If you go by what we would do if we could design our own bodies, there'll be a hell of alot of wings. Both feather and butterfly style ones, although probably ornamental. Gods, can you imagine how overworked the service bots would be cleaning up the feathers.
EDIT: Hell, if I could do that, even I would go for a pair of white feather wings for a couple of years.

And some mermaids. And pre-puberty body plans (it also works better with wings if you want to actually fly so there's that too).

I can also see some people going for tentacles, or turn into a distributed intelligence of a hive... =/
That actually happens quite a bit, including your last two examples specifically. In Excession, one ambassador to an alien species (the Affront, floating methane breathers who resemble jellyfish/squid hybrids) decides to trade out his human body for an Affront body for a while to better enjoy his time on their planet. In Matter, one SC agent becomes a member of an alien species whose name I don't remember that's basically a sea urchin with 20-foot tentacles that branch off into fine manipulators, which involves moving his mind to an artificial brain and setting up a distributed nervous system in the body with it.

One man in Excession (I think it's the ambassador but it might be someone else, it's been a while) has grown wings and really likes them, but he removes them and his neural lace while on a particular planet for the duration of a "back to nature" celebration when everyone gives up some sort of augmentation and enjoys being unmodified for a while. It's also mentioned in Matter that there are some more obscure and out-there transformations (like becoming a four-dimensional energy being) that are basically irreversible due to how different they are from the baseline humanoid.

Wings, gills, altered senses, and such are less common due to the prevalence of antigravity, the ability to modify bodies to different gravities and atmospheres at will, the ability to gland chemicals to alter perceptions, and so forth. The sort of people who would want to turn themselves into bird-people can instead simply use an AG rig to go flying for a while, which is more convenient than wings in everyday life and also comes with the ability to breathe in higher atmosphere, on-board AI navigation, etc. If they want to try wings until the novelty wears off, they can do that too, and I'm guessing that's why most people look "normal"--the gross physical augmentations can be duplicated in more subtle versions, so unless you're specifically going for a certain visual it's often easier to use the subtle version.