[nialo]

This is good, but not nearly as good as manually setting single character "keywords" for common searches.

[sathyabhat]

use the search enough times and you can use single character+ <tab>

[jarek]

Works well until you want to distinguish between searching en.wikipedia.org and en.wiktionary.org.

(While writing this I realized I didn't actually remember the exact domain Wikipedia and Wiktionary used... so I ran a "test" search on both.)