"About the mini PCIe mod on mac mini or iMac
I wanted to give this mod a try and purchased a lower cost SATA mini-pcie card (CONRAD-SATA-ASM1061 € 25.95) built around the (Asmedia, SATA3, PCIe 2.0) ASM1061 chip which is said to be well supported on OS X. (IIRC, PCIe card support reported with OS X 10.6.8+.)
   Sadly the controller wasn't even detected by the hardware - even lspci wasn't able to detect it, and booting the my early 2008 iMac with Ubuntu didn't gave better results.
(What OS X version was on the iMac? Card fully seated?-M.)
I'm a bit surprised. Maybe the board is DOA, but I don't have any other hardware to test it.
FYI, Matt.
(Update: here's his later reply:)
Yes, the card was well seated, I double checked that. I run OS/X Mavericks (10.9)
I went to a Commell MX-3132 (the SATA2 card used in prev mods here, see links below.-M.) and this time it was successful as expected. However, since my goal was making a Fusion Drive, I came across a big problem: the card isn't bootable. (SI3132 OS X Driver install required. But even if you could do it, I'd be leery of a Fusion drive from 2 different interfaces.)
I did not foresee that the kernel wouldn't have loaded the necessary drivers in order to access the second drive needed to mount the Fusion drive.
As far as I know there is no mini-PCIe card on the market that is also mac-bootable.
(None that I know either so far. My Mac Pro had a OS X natively supported (Marvel 88912SE) PCIe SATA3 card that also wasn't Mac bootable, although It was listed as bootable w/Windows PCs if AHCI enabled in bios. Ditto for the ASM1061 PCIe cards I think.-M.)

I guess that I'll stay with my current configuration : SSD on the internal SATA controller, mechanical drive in a external enclosure on the Firewire 800 port. I run this setup for some weeks without any issue and the performances are really far better for casual use than a standalone HDD on the SATA port, even with a small SSD disk (60GB in my case). The OS is generally extremely responsive and will make my old iMac last a few more years.
-Matt."

Thanks for the follow-up Matt. (If anyone had better luck with an ASM1061 mini-PCIe card mod, let me know. Include mac model/OS X version used. Also if eSATA case used is PM or not. Some cards have no PM support but ASM1061 lists it.) Previous mini-PCIe eSATA mod reports used a SATA2 Commell MPX-3132 card (SI3132 based) with (required) Silicon Image 3132 OS X driver install.
Here's links to previous posts on Mini-PCIe card mods in various Macs:

• Photo Gallery/Guide: iMac eSATA Mini-PCIe Card Install/Mod
• (2006-07) Mac Mini eSATA Card (mini-PCIe) Install/Mod
• Mini-PCIe eSATA Card mod in 17in MacBook Pro (not pretty)

2009 and later Minis -do not- have a Mini-PCIe slot airport card, but IIRC iMacs still do.
Last spring I asked if anyone had found a working USB 3.0 Mini-PCIe Card but no reports yet. (For anyone still needing wireless support after the mod, one option is to use an Ethernet to Wireless bridge.) Also curious if anyone does a working mod w/Mini-PCIe Broadcom BCM4360 based 802.11ac card.

(BTW: The 1st gen Apple TV also had a mini-PCIe airport card slot, which some owners swapped in a crystal video card for 1080P video support with 3rd party Media Center software mods.)
  

• Tip to Fix Maya performance on Late 2013 Mac Pro
• CrossOver 13.1 adds support for Quicken 2014 on OS X
• Jagged Alliance: Back in Action gets Mac & Linux Digital Distribution Release
• Apple's 1976 marketing plan included Apple Stores
• Wozniak: Apple Should Make an Android Phone

• iCloud: Mail server settings for email clients
• iCloud: Storage upgrades and downgrades
• iCloud: Storage upgrade pricing
  
  
• Apple TV (2nd and 3rd generation): Restoring your Apple TV
• How to identify counterfeit and imitation Lightning connector accessories
• How to view or print proof of coverage for your AppleCare agreement
  
  
• Pages for Mac: Setting the spelling dictionary
• Managed Client: How to disable Location Services in Mountain Lion and later
• OS X Mavericks: Updating disc-installed versions of Apple apps via Mac App Store
• iTunes Store charges on credit and debit card statements
• iOS: Using Reminders

• Beep wireless audio system: Pretty, but limited
• Beep is a Music Streamer Disguised as a Volume Control
• Review: Cambridge Audio DacMagic XS USB DAC
• Phones, Browsers, Search Engines Get a Privacy Overhaul
  (links to WhiteHat Aviator, which has a Beta OS X version)
• Chromebox, now for simpler and better meetings (google blog)
• Facebook permissions bug locks in malicious apps
• Review: QLogic 8300 Series Converged Network Adapter
• Review: Supermicro LSI SAS3008 mini-SAS HBA card
• Review: Kaleidescape Cinema One Blu-ray Player/Server ($3,995, ouch)
• Astronaut Captures Serene Scene from Space Station
• Hands On With Elder Scrolls Online

Wednesday February 5th, 2014 News
• Mac mini: How to remove or install memory
• Mac Pro (Late 2013): Installing or replacing memory (and more)
• Tip for Airplay mirroring freezes and dropped connections
• Why 30in DVI Cinema Display might show 1280 x 800 as max resolution
• Troubleshooting Apple TV playback performance
• OS X: How to connect with File Sharing using SMB
• iTunes: About iOS backups
• iTunes: Syncing media content to iPod
• iTunes 11.1.4 for Windows: Tips for Unable to install or open
• iCloud: Locating Reminders and Tasks
• Other News/Reviews/Tips/Op-Ed/OT:
  - Did Steve Jobs want Sony VAIOs to run OS X?
  - Review of Abbyy FineReader Pro OCR for Mac
  - PCMag list of Top Wireless Routers of Home
  - Pinnacle T1 PBAR 2000 Powered Sound Bar Review
  - Sony Negotiating to Sell Its PC Business to Investment Fund
  - Info on Xbox One Update coming Feb 11th

For links to older news pages, see the Archives.