MX  I got this with MacHeist, but I can't recommend it over Coda, which I paid full price for. As others have commented, the 1.0.x versions are just the bare minimum for site development.

Deal breaker for me: links have to be relative for the previews to work; absolute paths from the root directory are not understood even in Project view. If Espresso knows the root directory of my Project, why can't it figure out that links beginning with "/" refer to this root?

This needs to be fixed before I can consider trying out whatever other great features are touted by the developer. Without being able to properly preview my pages, there's no point going further. And there's no way I'm changing all the links to relative paths just to use in Espresso.

[I've been developing with Dreamweaver for 7 years. I don't expect Coda or Espresso to be as robust as DW, but this is a bare minimum feature as fas as I'm concerned.]  
(Version 1.0.5)

MX  I tried this app in Beta, and I'm now using it until my Tech department upgrades me to Dreamweaver CS4 (Subversion integration -- yes!). What I really like about Versions is the simplicity and the OS 10.5 interface. Simple to figure out for non-developers like me who only do about 3 things with Subversion: update, commit, and merge.

So it's the last thing that stall on my buying Versions for now: no merge capabilities built-in. Sure, I can merge by opening Terminal. But I want all-in-one super simplicity. Remember I'm a non-coder and I don't like to mess with command lining when it's at all avoidable.

I also use SmartSVN Pro which seems to have been built by coders for coders. It's not pretty, but not difficult to use, as I pretty much ignore most of the buttons and other features in the menus. SmartSVN is far more robust than I need, so I prefer to use Versions or DW CS4. Just hoping the "merge" gets added in a future update or upgrade.  
(Version 1.0.2)

MX  This looks like a fantastic app: fully integrated and excellent interface design to boot. Sadly, I've uninstalled the demo within minutes of looking at it because there is no way I'm going to get attached to it when the base cost for a single user is $1800! Knock a 0 off the end and perhaps I'd consider it. This is enterprise software for medium to large creative agencies, not for freelancers.  
(Version 9.0.4)

MX  Butterfly is a Windows app. Take a look at the header on this website.  
(Version 3.2)

MX  Doesn't adhere to the OS X GUI for opening and saving -- you can't dig into folders, you can only climb out. Once at the root level (or at the default level), there's no where to go. Pretty much renders the app useless. Too bad. It looks like an otherwise useful app.  
(Version 4.3)