I massively rate them. Had the Quad PCI for a few years now and it changed my productions overnight. What's good is you get all of the plugins installed and you can click demo to try any of them out immediately. Some emulations are exact (for example EMT250 reverb, Pultec EQ), some are close and have the correct tone but aren't the same as the originals (SSL channel strip for example), some are quite far away but are useful in their own right (mostly the tape plugins like the Ampex and Studer).

This is my full set:

Eventide H910 Harmonizer

AMS RMX16 (reverb)

Oxford Inflator

Oxford EQ

Ampex ATR-102

Lexicon 224

Studer A800

Precision Enhancer Hz

Precision Enhancer KHz

Precision Maximizer

Precision Multiband Compressor

Precision Limiter

EMT140 reverb

EMT250 reverb

Moog Filter

SPL Transient Designer

Roland RE-201 Space Delay

Roland Dimension D

Teletronix LA-2A Compressor

1176LN limiter

1176SE limiter

Pultec EQ

Cambridge EQ

DreamVerb

RealVerbPro

A good friend of mine has a lot of the real gear listed above, and even has a Series B SSL desk, so that guided me to the purchases, but also allowed me to do direct comparisons. I like the way they essentially re-build the machine's components in code (so they'll measure the input and outputs of all of the real components at various energy levels and then emulate them and 'plug' them together as code modules, pretty impressive.

Some plugins really take a lot of juice though, especially some of the newer ones where they're being more ambitious (Eventide, Studer, Ampex, AMX). I am considering getting an Octo to go alongside the Quad. That should last me a few years.

Offloading the plugin processing is very very handy as well, I rarely get the audio glitches because of a lack of CPU like I used to before.

So yeah, I recommend them highly.