Here’s your definitive manual’s complete comparison of Perforce to Mercurial:
Perforce has a centralised client/server architecture, with no client-side caching of any data. Unlike modern revision control tools, Perforce requires that a user run a command to inform the server about every file they intend to edit.
The performance of Perforce is quite good for small teams, but it falls off rapidly as the number of users grows beyond a few dozen. Modestly large Perforce installations require the deployment of proxies to cope with the load their users generate.
In order, I say, “bullshit”, “feature”, “buy a server, dude”, and “you’re doing it wrong”.
In fairness, the author admits up front that his comments about other tools are based only on his personal experience and biases, and the inline comments for this section point out its flaws. Still, it’s clear that his personal experience with Perforce was… limited. Also, he’s either not aware of the features it has that Mercurial lacks, or simply discounts them as “not relevant to the way Our Kind Of People work”.
I’m not criticizing the tool itself, mind you; I’ve tried out several distributed SCMs in the past few years, and Mercurial seems to be fast, stable, easily extensible, and well-supported. I’m switching several of my Japanese projects to it from Bazaar, and it cleanly imported them. It handles Unicode file names and large files a lot better, which were causing me grief in the other tool.
There are things I can’t do in Mercurial that I do in Perforce, though, and some of them will likely never be possible, given the design of the tool. [Update: for-instance deleted; it appears that if you always use the -q option to hg status, you avoid walking the file system, and you can set it as a default option on a per-repository basis. If the rest of the commands play nice, that will work. The real value of explicit checkouts, even in that example, is the information-sharing, something that devs often value less than Operations does.]