I've never had gear that I thought was garbage but I have bought things that ended up being useless purchases.
Trigger Finger - I bought this to enter drum parts and after using it once, I remembered my old Roland R-5 drum machine, dug it out of mothballs and have been using that ever since! I liked the feeling of the R-5 more for some reason. The trigger finger was an impulse buy and it sits, basically unused still in its box.
Behringer Bcr2000 - I have the Bcf2000 (fader) and it works great. I bought this based on how much I love the Bcf and still have not found anything I can use this for! All the knobs looked great but I still have no practical use for it! I've tried to program it with Sonar using Sonar's ACT thing where it's supposed to make it easier to program plug ins and stuff using a controller but 8 versions later and Sonar (based on what I've read on the message board) still doesn't have ACT functioning anywhere near what they've promised so long ago so it just complicates things and makes the Bcr more useless to me. Same thing as the trigger finger. It sits unused in its box.
A reprieve for the Digitech Vocalist II - I bought this years and years ago. Never could get convincing harmonies out of it and mothballed it for a long time. Eventually I took it out of mothballs and realized that if I tried to use it for effects and crazy vocal stuff instead of trying to get harmonies out of it (what it was intended for!) it's actually a fun little device and good for getting creative and strange things out of vocals!
The only real waste of money I've seen - but it wasn't mine (and I'll probably get flamed for this!) are Mac computers.
I was music director for a show that toured 8 months out of the year. On the first year of the show they had 13 macs backstage running the lighting, video, web streaming and everything and they just couldn't handle it. They were constantly locking up, crashing, freezing - everything Steve Jobs and mac fanboys claim they never do! Within 3 months of the beginning of the tour the tech director dumped all 13 macs and replaced them with PCs. The PCs did the job perfectly for the rest of the tour! I music directed that tour for 3 years straight, 8 months each year and up to my last tour it was still the same PCs chugging along running the entire show. Not that a hiccup here and there never popped up but if it did, the tech director could send a guy out to staples to get a part to fix it and have it up before showtime. In the end, based on seeing that first hand I'll never own a mac. Or as the tech director said, "Macs are only stable if you don't move them!" And before the mac fanboys attack me, this isn't a tour of kids in a van. It was a multi-million dollar tour with tractor trailers, full staging, lighting and a video production crew as well. The macs were encased in these fantastic road cases/racks that were built custom for them from the ground up and shock mounted here in NYC. I'm sure macs are great computers but hearing the tech guys backstage freak out as the macs systematically crashed or locked up taking the video or lighting with them put the fear of Steve Jobs in me! hahaha..
Besides, I have no PC or MAC brand loyalty. I love Commodore!