Fast and responsive UI rather then flaunt and animated. 

I have played for a while with the demo of the components.
What I noticed is that components with popup elements, such as ComboBox, DatePicker, TimePicker, ... have a small but visible delay, which becomes quite annoying with time.

Look at ComboBox demo, it seems there is some delay due to pre-configured animation effects on the control.  In slower browsers (take Firefox 6.0.2) the delay is obvious. 
The support for animation in general is a cool idea, but in most business applications it is not welcome by users who use application on a daily basis. 

Personaly, looking at the demo I am not sure if I can rely on kendoUI if my application designed for "do the job" rather then "enjoy UI".

I think it would be very nice if the demo has settings to disable all animations, to run it at full speed and demonstrate rich AND really responsive UI.

Add a way to check if the current AutoComplete value would be in the suggestions. Since the widget already searched for the value to see if it is in suggestions I would prefer to be able to check the result of that search. Something like calling kendoAutoComplete.search() but not have it affect the UI - just tell me if it was found or not. Is that possible?

I want to be able to alter the UI if the user has entered a value that is not detected in the suggestions to let them know it is not a valid value, and it seems silly to have to manually see if the value is in the datasource (and handle the filter variants 'startsWith' and 'contains') when that is already being done by the widget. So, I'm just looking to detect whether the search done by the widget found the value in suggestions or not.

In order to check dirty tracking, I would like to check the defaultSelected of the option of the MultiSelectControl. This now does not work.

Currently, the AutoComplete widget supports only a single separator value. It would be desirable to be able to fire an autocomplete action after multiple separators, which can be suplied as an array in the separator property of the configuration object.

Currently multiselect control has a change event only which is supposed to take care of add/remove event.
Please add proper events or pass info in the change event about what changed, so that developers doesn't have to write the same JS again and again.
See OnaBai's reply here

http://stackoverflow.com/questions/16608565/kendo-multiselect-trigger-an-event-when-an-item-is-removed

http://stackoverflow.com/questions/17653958/kendo-ui-multi-select-remove-selected-element-using-value

The autocomplete inorder to support search and at the bottome display all the results and the number of matched results,
there is need to footer template, like the facebook search autocomplete.

Right now other JS UI libraries allow the autocomplete dropdownlist to dynamically size based on the returned content. KendoUI sets the width to the width of the input box. I understand this looks nice but doesn't work for all business aspects. An example is my company needs to enter search criteria but the return results is the code and description. Since this can get longer than the input box the text is wrapped. This confuses users as they don't know where one item starts or ends. We use to modify the source files to fix this but the Q2 release changed a few things and stopped us from doing this.

The grid and autocomplete widgets really need no-data templates which display when the returned data is empty. The MVC controls were pretty good at this.

The option to allow new items to be added to the list, as opposed to items exclusively in the datasource.

For example see this: http://jsbin.com/iXEtonO/4/edit, only built in

When using IE10/11, it natively supports the clearing of input element so essentially when hovering over a Kendo ComboBox with a selected value, this is the end result:

http://i1256.photobucket.com/albums/ii484/vobreshkov/KendoComboBox_IE.png?t=1376577876

I am constantly getting requests to have such way (or adding an extra menu item) to my combo boxes to allow users to click on something and clear the selection. Please consider extending similar functionality to the combo box that is available on all browsers.

There are a couple of things that are very common that I would like to add buttons for.  The first is for clearing the value and the second is a + for adding new items to the list.

The + button is an important one from a usability standpoint.  Quite often the combo/dropdown is populated from a list that is managed on a separate page.  It is too cumbersome to have to use stop entering and go to the admin page to add the new item and then come back to add whatever they were working on previously.

I know I could simply add a button beside the widget but this just doesn't look as nice as it being built in.

Currently it seems that kendoDropDown only supports select elements with options and not optgroups. Would like to see this widget support select elements with both optgroup and option elements.