I haven't seen a formal article on it yet but I would follow these steps:

1. 
   
2. Go to K2 for SharePoint tab in Central Admin and run through each link in the feature management and deactivate each feature for each site collection (that you have activated the features on).
   
3. Retract and then delete the K2 solutions from Central Admin > Operations > Solution Management.
   
4. Uninstall the K2 for SharePoint components from each WFE box
   
5. Uninstall the K2 for SharePoint components from each CA box
   

I'm trying to retract all K2 components:

k2 for sharepoint - core components.wsp
k2 for sharepoint - management console.wsp
k2 for sharepoint - process portals.wsp
k2 for sharepoint - reporting web parts.wsp
k2 for sharepoint - web designer.wsp
k2 for sharepoint - workflow core.wsp
k2worklistwebpart.wsp

But some components reset to deployed... Could that be because there is a lingering site that still has the k2 feauter activated? Is there anywhere where I can see a report of all activated features on each sites?

Thanks!

Martin 

This question is more SharePoint related but I found the following references to be useful.  There are probably other articles but these were the first few that popped up.

http://social.technet.microsoft.com/Forums/en-US/sharepointadmin/thread/e497ac48-0c8e-4eb8-9c87-94a525d8e73e/

http://blogs.edwardwilde.com/2009/12/17/programmatically-determine-is-a-feature-is-activated-or-even-installed/

http://get-spscripts.com/2010/08/bulk-deactivate-feature-and-remove-farm.html

Well - I decided to just run the uninstall since I thought the feature was removed...

When I ran the uninstaller - it did automatically retract and delete all of the K2 Web App features and said that the uninstall was successfull. But now, Sharepoint is down completely. Getting this error:

 Server Error in '/' Application.

<!-- Web.Config Configuration File -->

<configuration>
    <system.web>
        <customErrors mode="Off"/>
    </system.web>
</configuration>

<!-- Web.Config Configuration File -->

<configuration>
    <system.web>
        <customErrors mode="RemoteOnly" defaultRedirect="mycustompage.htm"/>
    </system.web>
</configuration>

Runtime Error

You got to turn off the custom error handline to see the actual error (as per the instructions on the page).  This will hopefully indicate the actual issue.  If this is urgent, I would also suggest logging a support ticket to see if a support engineer is able to assists you on this.

Well - thankfully this is in my Dev environment so it's not that urgent. But this is practice for removing it in prod.

I removed the custom erros and here it is:

Configuration Error
Description: An error occurred during the processing of a configuration file required to service this request. Please review the specific error details below and modify your configuration file appropriately.

Parser Error Message: Could not load file or assembly 'SourceCode.SharePoint.WCFHosting, Version=4.0.0.0, Culture=neutral, PublicKeyToken=16a2c5aaaa1b130d' or one of its dependencies. The system cannot find the file specified. (C:InetpubwwwrootwssVirtualDirectories80web.config line 106)

Source Error:

Line 104:      <add name="RoleManager" type="System.Web.Security.RoleManagerModule" />
Line 105:      <add name="Session" type="System.Web.SessionState.SessionStateModule" />
Line 106:      <add name="WCFVirtualPathProviderRegistrationHttpModule" type="SourceCode.SharePoint.WCFHosting.WCFVirtualPathProviderRegistrationHttpModule, SourceCode.SharePoint.WCFHosting, Version=4.0.0.0, Culture=neutral, PublicKeyToken=16a2c5aaaa1b130d" />
Line 107:    </httpModules>
Line 108:    <globalization fileEncoding="utf-8" />
 

Source File: C:InetpubwwwrootwssVirtualDirectories80web.config    Line: 106

I think it might be a stray configuration entry that wasn't removed by the uninstaller.

Backup your web.config.  Remove the entry and refresh your page again.  It should come back up.

That's great! It worked!

Is it safe to say that the uninstaller takes care of retracting and deleting the web app solutions?

Thanks for your help!!

Seems to be the case.  However, I have spent more time installing K2 than uninstalling K2 so my memory is a bit fuzzy on this one :)

Ok cool! Well thanks a lot for your help!

I have verified the answer you provided me! :)

Cheers.