Most of my regretted tech purchases come from me being cheap:
My first 2 computers I built using some POS Raidmax $30 cases that had crap for airflow and were poorly constructed. I only bought them because I thought the looked cool

. One I still used in spare computer, but the other I was luckily able to sell to a friend and bought myself an Antec 300.
When I decided to finally get a "gaming" mouse I went really cheap and bought a Gigabyte one for about $25, which started tweeking out and moving by itself after about 6 months.
And several other items like HDD enclousers that broke after 5 months and things like that.
I'm usually too poor to jump on brand new tech or games and have to wait for them to go on sale or the price to drop, and by then there is a slew of reviews to tell me what to stay the hell away from. So being cheap and poor saves me some heartache, but also causes me to buy POS items, then turn around to buy quality items

.
Sadly where I work invested heavily in Zip disk and drives, using them to back up data before DVD/CD tech or HDD tech improved. So we have a 1/2 file cabinet draw full of zip disk and about a dozen zip drives laying around

.
Worst one my best friend ever did was about an Windows ME computer, and to make it worse the RAM stop being produced about a year after he got it (I believe it was made by Rambus), so then he couldn't even upgrade the thing and try for Windows XP on it

.