Krunner is KDE's launch utility that opens whenever you click Run command... or press ALT+F2. In addition to just launching applications it can do many other things such as calculations, doing dictionary lookups and searching through your files. When your ALT+F2 dialog is becoming slow, it is recommended to review all the plugins it has loaded. By just pressing ALT+F2 and then clicking on the wrench icon, you can go through all the plugins it loads.

A couple of examples you can probably do without:

• Activities: Unless you actively use plasma's activities.
• Bookmarks: Unless you use Konqueror's bookmarks.
• Desktop search: Unless you have desktop search enabled.
• Devices
• Dictionary
• Kdevelop sessions
• Nepomuk Desktop Search
• Plasma desktop shell
• Powerdevil
• Recent documents
• Windowed widgets
• Windows

Many of the above-mentioned plugins are plain useful, therefore make sure to review everything before you disable anything.