PETERNSTEINMETZ  I've been a long time user of Interarchy (and prior to that Anarchie) and liked the older versions rather well.

I have to recommend CyberDuck instead these days. Although Interarchy transfers are fast, the developer who acquired it really isn't maintaining this. The 9 update appeared to mostly a reason for the new developer to charge everyone something.

The new UI is not the most intuitive, in my opinion.

Cyberduck is perhaps not as polished and not as fast, but it is free and is maintained.  
(Version 9.0.1)

KIDDAILEY  This FTP client is awesome.

It supports FTP, SFTP, SSH, SCP, WebDAV, WebDAVS, AmazonS3, AmazonS3S, HTTP, HTTPS, and File/Local.

The interface is excellent and easy to use. I disagree with the other comment made here -- I think Interarchy 9 is without question, the "prettiest" of all the FTP clients.

Bookmarks are easily accessible and can be organized any way you'd like.

The mirroring functionality is top notch, and I use it to easily mirror two file repositories of 40GB+ each without any issue. One of these repositories is standard FTP and the other is AmazonS3. The ability to schedule the mirrors makes for nice automation.

I've also used the SSH FTP support to manage files on my iPhone (which shows up automatically in Interarcy thanks to Bonjour).

The developers are some of the most responsive and receptive I've dealt with and I saw a number of my suggestions implemented during the course of helping them with the beta releases for this version.

I've used (and purchased) many FTP applications over the years: Cyberduck, VicomFTP, Transmit, FileZilla, RBrowser, etc. etc. and they all fall short.

Interarchy 9.0.1 has still got a few quirks but it is, in my opinion, vastly superior to the other available clients.  
(Version 9.0.1)

GERBER  9.0.1, I am happy to report, fixes all the critical bugs in the 9.0 release. It's rock solid, now, just like it always used to be. This update also adds some minor, but very helpful, features.

Interarchy remains the Big Dog of file transfer clients. While there are many more applications that handle the same tasks, some of which are, perhaps, prettier (Transmit), simpler and easier to learn (Fetch), or are free (Cyberduck), no program has the power and depth of Interarchy.

Version 9 has greatly cleaned up and simplified the interface. The new sidebar, better tab management, and the path bar at the bottom of the window are great improvements and make it much easier to browse around a large directory tree.

The ability to browse the Finder in a tab gives it the ability to have a dual-pane-like view, while still maintaining the simplicity of a single window most of the time. You can also copy & paste from the Finder to Interarchy, which is very handy, but unfortunately doesn't work in the other direction. (Although drag & drop does) You can also copy & paste within Interarchy, even to transfer files to other servers.

The SSH connection type is truly awesome. Directory listings with lots of files pop up instantly. Mirror and backup syncs (one of Interarchy's major strengths) are far faster since it can crawl directories incredibly quickly to find differences. Whereas I'd avoid mirroring certain complex sites since it took so long to find changes and run the mirror, I now find it entirely painless.

There's also some very nice additional spit and polish including some menu rejiggering to make it a bit more standard, some new preferences, interface clean-ups, etc.

Then there's all the usual Interarchy goodness: File converters for automatic encoding/encryption/compression of files on upload; support for nearly every file server protocol; Net Disks and mirrors for easy synchronization between your Mac and a server; contextual menus and droplets for easy on-the-fly file transfers; and an excellent AppleScript dictionary.

Interarchy is definitely not for everybody. I highly recommend testing it and its competition before buying it. But if you need some of these unique features, or if you want hassle free and automatic synchronization, mirroring and backup, there's nothing better.  
(Version 9.0.1)

META  I love Interarchy 8, but version 9's added features just don't seem to justify the upgrade price for me--particularly not given that the upgrade price for Interarchy is the same as the price to buy a full license of a comparable product like Panic's Transmit.  
(Version 9.0)

GERBER  The new SSH-based transfer protocol is amazingly fast. It does some sort of magic compression, so pulling files down is speedy as all get out, and comparing directories for mirroring transfers is lickety split.

Unfortunately, yes, it's got a lot of bugs that, strangely, weren't present in the recent beta releases.

I'm holding off on a review until 9.1 comes out and fixes these bugs.  
(Version 9.0)

GCOGHILL  Interarchy looks like it could be pretty slick (and I love the UI) but the lack of a dual-pane file browser kills it for me. I'll have to give it another go, but once you go dual-pane, it's hard to go without that feature.  
(Version 9.0)

TVALLEAU  Wait for 9.1

Unfortunately, this version is not ready for prime time. It crashes constantly. (Their forum is full of complaints.) There is no help; you cannot add a folder to the bookmark bar w/o crashing; adding a local file bookmark crashes it; the net tools are gone.. the list goes on.

This is very weird: Interarchy has always been a strong, reliable client... this release (9.0) isn't even ready for beta status, IMHO.  
(Version 9.0)

ISILVER  yeah, yeah, I know ... sorry!

"A free upgrade is offered to all users who purchased Interarchy on or after February 1, 2007 and will be notified automatically via email."  
(Version 9.0)

ISILVER  I think the "special price" of $29 for the update is a bit extravagant - after purchasing v8.5.2 last year (for $39), there has only been a few small bug fixes before the release of v9. Now if I want to update, there is only a $10 discount.   
(Version 9.0)

JPALME  I still have problems with Interarchy forcing me to type a password every time I access a certain remote site. I have communicated a number of times with the Interarchy developers about this, and followed their advice, but the problem persists. If I had not been for this problem, I would give highest score for Interarchy as a super FTP program.  
(Version 8.5.4)