Here is Nitin's list of essential search engine features for the future:

• Personalization (but without storing personal info )
• Social Input / Wisdom-of-Crowds (which has its pitfalls )
• Semantic Processing: of both, the query AND the content (will this let the Search Engine find Answers that we never knew we had?)
• Parametric Input: including freshness, source and domain-specific
• Rich content types: audio, video, images, news, blogs, ‚Ķ
• UI enhancements: better visualization of results
• Findability support: notifications of interest, a database of intentions
• Follow-up: results clustering and drill-down
• Repeat queries (as Greg Linden points out )
• Trusted sources: e.g. a slider to select the level of trust, from high to low

Check out the full article and leave a comment on AltSearchEngines about what you think a search engine is - and what it'll be in the future.