Pros: This is high quality bare-bones PC. The components are well laid out and assembly is straight-forward.

Cons: No USB 3 on the back.

Other Thoughts: While not silent this is very quiet and it is not designed to be a HTPC - it is for specialty applications that require a compact PC with some legacy hardware (serial ports), multiple nics, etc. It worked out great for my needs and have 5 of them running in various locations with no issues.

Pros: Very small but easy to assemble, supports the latest Haswell processors - don't go over 64W. I used i5-4440S. Runs fast and quiet if you get lucky with the fans on your unit. The dual fans look cheap, but seem to be the standard 50mm size and should be easy to replace.

Cons: One of the two I ordered was DOA. Waiting for the RMA process, had to pay rather high return shipping. The DOA machine had a noisy fan it.

Other Thoughts: I ordered two of them for HTPC use, to be built with identical i5 Haswell CPUs, Micron mSATAs and 8GB memory. One was DOA, would not POST. The fan on the dead unit was very loud and whiny at start. The other unit was easy to build, is quiet and it works great. 4 stars overall.

Pros: Quiet (but not silent) small form factor PC. Easy assembly.

Cons: No USB3 on back panel. Fans are audible when PC is at arm's reach.

Other Thoughts: Unlike the other reviews, I did not find that the fans were too loud. This is not silent like my Mac Mini, but you could not hear this from across the room. I got this with a $99 i3, stuck an old laptop drive and a couple sticks of RAM from an old mac, and I had a great HTPC for less than $300.

Pros: The XH81 comes with the quality construction that's known with the XH61V that I've had for some time. The support for Haswell made this unit worth waiting for. However... if they don't fix the cons, this is likely my last Shuttle.

Cons: I'm writing this review next to a noisy XH81. It is loud; even at a cold idle. It is un-Shuttle like. I contacted Shuttle Support and they confirmed that the fan speed on their lab's XH81 also runs at 2600 RPM. Then, they went on to explain that maybe my fan is blocked or the fan size dictates the high RPM. But their fan speed and my fan speed is the same 2600 RPM.

Here's my case for them to go fix this so other customers don't have to be annoyed:
Every Shuttle I've owned over the last decade has had an RPM of approx 1200 for the setting "Ultra-Low" and are quiet as a result.
Comparing the Fan Speed settings for XH61V vs XH81:
Ultra-Low Speed: XH61V:1200RPM XH81:2600RPM!
Low Speed: XH61V: 2400RPM XH81: 2600RPM

The XH81's Ultra-Low and Low Fan Speeds are the same! BIOS bug? Likely.

Based on that pattern, I would think that ShuttlePC Engineering back in Taiwan should made changes to their BIOS code to restore the proper Ultra-Low speed for the XH81 to 1200RPM. And thus, restore faith in their customers.

Other thoughts...
I've observed the CPU temperature through a range of workloads and also confirmed that heat is transferring through the heatpipes as designed.

Other Thoughts: If you're having trouble with the USB3.0 drivers you download from Shuttle's driver page, it's because they packaged the wrong thing in the zip file. Shuttle Support pointed me to getting the USB3.0 drivers from the DS81 download page.

Pros: Having had the great XH61V, I was really looking forward to the XH81 for the expected build quality and Haswell support.
The XH81 has the same high quality construction and ease of installing component while maintaining a small form factor.

Cons: To my dismay, the XH81 is much noisier than the XH61V. I called Shuttle Support and had to strongly suggest they escalate what could be a BIOS issue.

On the XH61V, the fan's Smart and Ultra-Low Speed runs at 1300 RPM. At Low Speed, the fan spins at 2400 RPM.

On the noisy XH81, Smart and Ultra-Low runs at 2400 RPM while Low runs slightly higher at 2600 RPM. The support Tech at Shuttle also confirmed that his XH81 runs at 2400-2600 RPM. The Tech thought 2400 RPM was normal. In the 10 years of owning many Shuttles, 1100 RPM is normal for Ultra-Low speed.

The CPU temps are roughly the same. It's not blocked fan nor is it the lack of thermal paste. I would have think a little adjustment to the BIOS code would correct Ultra-Low back down to 1300 RPM where one can barely hear it.

A message to Taiwan Engineering: Please fix this quickly. I would like to not have to return this or place it far away in a closet like a PC from 1990.

On another note, don't waste your time troubleshooting USB3.0 missing drivers: The XH81 USB3.0 Driver download from ShuttlePC has been erroneously zipped with the wrong installer. That installer does not provide drivers for USB3.0. Instead, go to the DS81 download page to get the USB3.0 driver.

Other Thoughts: Terribly disappointed in ShuttlePC's lackluster commitment to quality control and user experience.

Inside the XH81:
http://www.newegg.com/Product/Product.aspx?Item=N82E16819116988

http://www.newegg.com/Product/Product.aspx?Item=N82E16820239390

http://www.newegg.com/Product/Product.aspx?Item=N82E16820147318