I usually vacuum my wall-to-wall carpet, a lower plush type, with my central vac and power head.  The central Vac is an imperium true cyclone vented to the out side.  My power head is a Lindhaus.  My home is almost two years old and every time I empty the central vac, it is full of carpet fluff and cat hair.  Yes, we do have a cat!  When vacuuming with the Lindhaus, I always have to have my back-stroke pulling the nap of the carpet up.  If I try to "push" the nap up with my forward stroke, the power head skips along and does not effectively groom the carpet into the up position.  To get around this, I always make sure I have the back stroke pulling it up.  Over almost two years, we are starting to see some wear patterns in the carpet.
 
Today, I changed the bag on my Sebo X4 to ready it for a friend to borrow while I tune up her crummy Eureka, and fish a stuck sock out of it.  After I changed the bag, I decided to give it a run on my wall-to-wall here.  It grooms the carpet well no matter which direction it is pushed or pulled across the carpet.  Also after I vacuumed the family room, approx. 500 sq. ft. I opened it up and looked in the bag.  There was a lot, I would guess maybe 1 cup total, of carpet fluff.
 
So, my question.  Does the Sebo do that much better a job than the Lindhaus on the central vac?  Ever since we lived here I have used the central vac, it has very, very strong suction and I like the idea of all the allergens going outside.  My alergies have not been as bad since we lived in this new house.  However, I don't want to be using a vac that is going to shorten the life of my carpet, or, just not do a good job.  Any advise?  
 
I remember back to my mom's Dial-a-Matic and Concept Two with those metal/plastic beater bars on the agitator.  Neither the Sebo or the Lindhaus have those.  Are they agressive enough for our carpet?  Please let me know your thoughts and what you would do given my equipment and situation.  Is there a better power head for the CV?  Please help!

Does the x4 have auto height adjustment,or manual adjustment like the stealth / lindhaus power head?
 
  O.T.

As an experiment, you might try vacuuming with the CV/Lindhaus, but only (if possible) with the powerhead brush motor running.  That way, suction is not a factor, and you can see if the brush still "skips" against the carpet.
 
Does the Lindhaus make any unusual sounds when pushed?  I believe those powerheads have cogged belts and shouldn't suffer from belt slip.
 
Yes, the X4 has auto heigth adjustment via a servo motor adjusting the centermost wheel.
 
The WW brushes I mentioned earlier are Manual adjust  (though for some reason, Bosch left manual adjustment off their version.).

There is a distinction between cleaning and grooming rugs (as the last poster states).  Most vacuums will do the first (more or less) fewer do the latter and even fewer do it well.  Cleaning is getting the surface and embedded dirt out of the rug.  Grooming is lifting and separating the rug fibers and restoring the rug's original resilience.  The better a vacuum grooms, the easier the dirt, especially deep down embedded dirt, is removed.  Why?  If your vacuum loosens and lifts the matted down rug fibers, it's easier to remove the dirt inside the rug.  And the rug will not wear down and out as quickly.
 
The best, bar none, for cleaning and grooming rugs is HOOVER: The GOLD standard.  Lifts and separates the carpet fibers.  And cleans.  
 
I keep an area carpet, same as my house Mohawk wool low level plush, in my garage and park my Ford Explorer XLT on the carpet.  The vehicle weighs about 4500 pounds, maybe more.  After sitting over night, the carpet is matted down from the tires, especially the front tires.  The least expensive HOOVER upright TEMPO, $60 rated no 8 by Consumer Reports in October 2006, will restore the carpet's resilience in a few passes: Grooming.  At the same time removes any dirt on the surface and embedded.
 
Try the same with the more expensive vacuums.  They'll do the job, but with more passes and not as well.
 
I vacuum my house rugs daily with an upright  HOOVER WT Supreme (MSRP $120).  The look and feel of the rugs (when you walk across) is the same today (7 months after the rugs were installed) as new.  A year from now,  2 years from now, 10 years from now, I expect the same.  My household includes my dear Wife, a 9 year old English yellow lab, and me.  The dog sheds all the time.  I have 2 grand daughters who visit daily with my daughter and/or son-in-law.  The oldest, 2 1/2 yo, loves to run, jump, bounce, lay and play on the rugs.  Her toys and playing on the rug mat the rug down.  My dog laying on the rug mats the rug down.  No problem.  A few quick passes with the HOOVER WT and voila, restored to new (and cleaned).  Grooming.  Lifting and separating rug fibers and restoring natural resilience.
 
Carmine D.

If I remember right, Lindhaus offers different density brush rolls for their vacs.  If so, you could upgrade your Lindhaus brush with a softer brush roll for far less $$$ than a new powerhead.
 
The DC17 Dyson apparently has a brush roll more suited to American rugs than the older, Euro-oriented Dysons.