Is there a place to review journals or conferences?

There are a few sites that do this:

• SciRev
• Journalysis.
• HelpMePublish.

Of these, I think SciRev is the most active, but I'm not certain about this. That said, in my experience, the actual rating information on these is not of much value. Uptake is pretty slow, and most of the reviews I've seem to just very high marks indiscriminately. As a result, you can't infer too much from the tiny sample sizes available. The information about time to result, review quality, etc. might be useful in principle, but in practice again you've got tiny sample sizes and probably a selection bias as well in terms of who submits reviews -- though I don't know which way this selection bias would go.

Nature wrote a news piece (not paywalled) about these sites in early 2015.

I would like to provide an update on what Corvus already wrote back in 2015. The URLs provided are not alive anymore, it is only SciRev that I could find, on a new domain: SciRev.org

As Corvus remarked, quality scores are questionable, but I found review period feedback useful. SciRev still has very small sample size for journals of my interest, but even with 3-4 reviews, coming from different users - you get at least some idea on the timing. In my perception, reported time periods tend to converge - therefore, it can serve you as somewhat valid indication.