q1: how soon will we be able to have alpha transparency workin for skins??
In the preferences, in Interface --> General --> Skins, you can check "Enable transparency effect". The behaviour is controlled by the Theme.alpha and Theme.movealpha parameters of the skin (cf. documentation). "movealpha" works rather well, but if "alpha" is set to a value lower than 255, resizing really sucks, and I don't know how to fix it. That's why the option is disabled by default in the preferences, to ignore the actual values of "movealpha and "alpha".
(Note that it only works on Windows).
Edit: well, trying that again on the default skin, it's not so much horrible. Please test it and report the issues, if everyone is fine with it it could be enabled again, and we might also provide a way to force the alpha value of a skin...
q2: is it possible to have a "center" positioning... (some of the skins im workin on require having buttons etc positioned in the middle... but when resizing... it all gets screwed up)
If you don't mind that your controls are resized, you can have use topleft and rightbottom to stick the left side of the control to the left side of the window, and the same for the right side.
There is currently no solution if you want your control to be centered and also want it not to resize with the window. We might add another attribute for that, but we need to find an expressive and powerful way to do that (adding a "center" attribute is not nice, what if you want to put your control at 1 third of the window width?)...