For me it's been mostly smooth after a clean install, but there are a few things that make me deeply regret not staying with Mojave. The main issue is that I'm having nothing but trouble with iCloud syncing ever since. Initially when I installed Catalina, it took nearly 3 hours for my MBP to even start trying to sync my files. I keep a lot of 3rd party software licences, Alfred workflows etc. on iCloud and I had to manually download everything from www.icloud.com to get my machine setup. Today I've been waiting for 4 hours for 4 PDFs to upload and almost 24 hours for a 9 track album to upload in Music. I've tried forcing the 'Update Cloud Library' function in Music and it runs the process and completes it but the files don't sync. There are no error messages (keeping with Apple's recent abandonment of many key error messages, as raised by Marco Arment on Twitter). Notes in the Notes app can take anywhere up to 30 minutes to sync as well. iCloud sync is so pivotal to my workflow, using two MBPs and an iPhone, and this is driving me crazy.