I have had buyers call me for advice to protest their taxes.   In Denver it is filed electronically, and usually have good success.

Yes I have. Also, did a few for a couple of clients & was successful but I presented them in person with pictures not online. Best of luck.

I've done this a few times - unsuccessfully I might add

No, just the old fashion take a number and wait.

Not personally - but I know two people who challenged their assessment.  Neither was successful.

I have not been very successful doing this in person either.

I've filed and won a couple appeals, but I went in person with photos.  I find some things are better done in person (and it's only a 20 minute drive to the county recorder's office here).

Hi Richard - Every 2 years when there is a reassessment, we work with a bunch of our clients, providing comps for their appeals. We always recommend that they go in person to the assessor's office - it has been our experience - anecdotal but convincing - that an in-person appeal has a better outcome than using the on-line system.

Get calls all the time, I tell them the strategy that worked and wish them luck,

Yeppers - they seldom believe anyone but themselves

Yes, I did this. Very educational too. It is easy to file. Weeks after I filed, I got a call from the assessor stating that we can settle this now and not have to go before the appeals board if I like. I said sure. He then shared all his comps to support his position and asked me to share mine. He said it all comes down to comps even though you can explain and discuss all the side issues. He made a point to emphasize how long he has been doing this making experience a key credible issue. I hit the ball back saying I have been in Real Estate for decades & my opinion is professional too. We finally came to a figure we both could accept. Very sharpening experience for me

More and more people are going through this process to lower taxes.

Not familiar with an online appeal process. Usually done at the county level.

No recent experience.

No.

no experience - good luck

filing a tax assessment appeal is usually a losing battle.... 

In Los Angeles County, California -- it's a print/mail-in process and yes I know some home owners who have been successful in appealing property taxes when there has been a perceived decline-in-value.  More information can be found here.  

Looking forward to reading the answers...