None yet. Though I am still young, on my third system, and have only been in the hobby for three years. So it is doubtless I will make some mistakes in the future! But so far all up my upgrades have been vast improvements. I've been mostly upgrading from lesser components to better ones. So all in all I've been most satisfied thus far!
I imagine a lot of the responses you are going to get are one of two things
1. Did a lateral 'upgrade' to a comparable item. Didn't like the change in sound.
2. Bought something based solely on someone else's opinion (magazine, internet review, internet buzz, dealer buzz, etc) without extensively auditioning in one's own system first. And was let down as a result.
I imagine a lot of the responses you are going to get are one of two things
1. Did a lateral 'upgrade' to a comparable item. Didn't like the change in sound.
2. Bought something based solely on someone else's opinion (magazine, internet review, internet buzz, dealer buzz, etc) without extensively auditioning in one's own system first. And was let down as a result.