I eventually test out all of my powers, and then integrate them into my set. The other homebrews I really like I will also test at some point. I've authored over 200, and of that I have tested out about 150-160 of them. I'm making mockups of the others I've created to get tested over the next few months. My homemade set of Cosmic has 316 alien powers in it at the moment. As you can imagine, a majority of those are homebrews, and of them, most are my own. I have over 100 homebrews that are thematic... so, there are moon aliens, lucre aliens, tech aliens, and several that are part of closed sets.. like the Lovecraftian Encounter aliens, and those for Cosmic Dune. I'm almost up to 100 aliens that are not dependent on any expansion or variant. I'm hoping to hit that number in the next 12 days (before my 40th birthday!). I don't bother posting all of the ones I've created here.... it would get to be overwhelming... but the new ones I think up that I find interesting- I go ahead and place here.
I'd be interested to hear other people's plans or history of creating new aliens that they actually use, or other homebrews that have made it into their sets.
I used to use Ken Cox's postscripting to print stuff out... it looked a lot like the Eon styles components. My homemade set I use now uses my own templates for everything... but I have started printing FFG-style aliens to add to that set... I just create them in Photoshop with a template I made.