Status of the issue: we identified a few issues regarding the Source and Design views performance. We are working on the fix, but unfortunately, I cannot give you any timeline. Here is what we know about:

a. Design view typing in certain files can be affected by too frequent sync from Designer to Source view. There is no workaround. 

b. Source view performance may be affected by too frequent updates of JScript intellisense data or by updates to the Properties window.

In (b) you may try turning off intellisense in Tools | Options | Text Editor | HTML | General -> uncheck Auto List Members and see if performance gets better You may also try switching off validaton in Tools | Options | Text Editor | HTML | Validation. Try also closing properties window.

In any case - I would like to collect more information since there may be other cases. Feel free to e-mail me your repro steps and, if possible, repro page at mikhaila-at-microsoft-dot-com. Minimal repro is, as always, appreciated. Please provide the following information:

1. Are there any themes or style sheets attached and if performance gets better if you detach the style sheet or disable theming.

2. Is performance better when properties window is closed.

3. Does delay depend on which element are you editing (i.e. how long is the element properties list)

4. Is performance better when there are fewer controls with ID attribute?

5. Is editor faster when there are no client script blocks in the page?