Bridging amps, Good idea or bad idea?

I own a Cambridge Audio 840W, which can be bridged, which makes each amp a 500w mono block as opposed to a 200w stereo amp. That's 1Kw PER CHANNEL! Are there any downsides to doing this? Will there be added distortion, or will it chnage the sound any negatively? I already high pass my speakers because I use a sub so they only get 80hz+ as it is.
I found this information about bridging amps on the Audio Asylum FAQ. You might find it useful.

Audio Asylum - Biamplification Basics

Bridging (also called monobridging or monoblocking) is the summing of two channels of an amp to give one higher-powered channel. An amp normally rated at 100W might deliver 300W to 400W when bridged. Because of the summing however, the load on the amp is seen as half of its normal value. In other words, an 8-ohm speaker becomes a 4-ohm speaker load, and a 4-ohm speaker becomes a 2-ohm speaker load. Speaker impedance ratings are nominal only. Actual impedance may dip to a much lower value through part of its range. When an amp's current load has been doubled due to bridging, it can often fail to provide the required amount of current into the load. Sonic effects include harshness in the midrange and highs, and thin bass. In almost all situations therefore, biamping with similar amps will result in better sound quality than bridging. Bridging is best left to professional sound-reinforcement applications, where sound quality is secondary.

Good Luck and I hope that helps!
It's true what Kurt's link says. Most amps when bridged cannot drive low impedance loads. Your owner's manual probably states what load you are limited to when bridging.
The damping factor is also cut in half.
More power, (on paper), and less bass.
I've tried it with Adcom & Parasound.
Both brands sounded better using just one channel of each amp.
That allowed the whole stereo amp transformer to supply one channel...
Try it in your setup.
The 840W is rated for 800W bridged into 4 ohms and the sub will help, particularly with an active xover. When you get close to the edge, even the wrong speaker cables can push it over. Depends on the speaker load... resistive, capacitive, impedance...

How about power? That's 2 X 2400W (at ear shattering levels), or 40A @ 120V.

Doubling and quadrupling isn't much of a absolute SPL increase but that's not what it's about. Closer to the point is whether that much power, without the low bass requirement, will benefit your speakers. I could understand for Maggies or Carver A3's.
The different times I tried it,I was disappointed with the results of the sound.Transparency,cleanliness,distortion, and changed frequency response just to name some of the drawbacks I encountered.
i was wondering the same thing myself . i had always heard that bridging was not a great idea but i have read that many users of the vac stereo amps that i am interested in trying : specifically the vac phi 300.1a and the vac phi 200 bridge them all the time . they apparently were designed to be bridged with a flip of a switch . i wondered if that makes these vac amps less than ideal when used in their monoblock mode . evidently the manufacturers don't believe there is any problem with bridging . still i wonder ...
The different times I tried it,I was disappointed with the results of the sound.
My experience exactly. Always preferred one of the amps alone in stereo as opposed to two of them bridged. Now biamping with two amps did seem to yield improvement. Of course you need an extra set of speaker cables.
If you search for on-line reviews of Spectron amp owners then, as far as I know, without exceptions - all states theat then they move from stereo mode to monoblock sound quality more then double.

I am also one of these. Spectron attribute this achievment to the proporly build power supplies most of all and high tolerance of its parts. Simon says that when you switch from stereo to mono - you hear practically distortion-free music.... I am not EE, will not argue techno stuff but I know what I hear. Improvments are STUNNING !!!!!!
Not all amps suffer when run in mono. If an amp is a high current design from the beginning there should not be a problem. ARC Classic 120's are essentially a pair of Classic 60's converted to mono and a pair of Krell KMA 160's is two KSA 80's converted as well. Likewise with many of Krell's and ARC's earlier designs. Many others do this also.