SharePoint Server 2010 Search represents an important upgrade to the existing search for SharePoint 2007.

Following are the features included with the SharePoint 2010 Search
No more 50 million items limitation:
FAST
provides powerful capabilities to index hundred millions items, so no more SharePoint 2007 index limitations.

Query Based Search:
Now we can use AND, OR, NOT keywords in search query

Wildcard search:-
Now we can using * in search query i.e., when you search for sha* you will all Indexed results with starts with sha.

Faceted search/Refinements:
Refinements are shown in the panel to filter the results (by tags and metadata). This functionality is supported in the Sharepoint Server 2010 standard edition and above

New search Web Parts:
Many search-related Web Parts that enable power users to create customized search experiences that implement automatic filtering, best bets, a refinement panel, featured content or offer pre-defined queries

Social people search:
Phonetic name matching (returns names that sound similar to what the user has typed as a query & all variations of common names, including nicknames); exploring results via name, title, and expertise; include real-time presence through Office Communication Server

Social distance:
SharePoint builds a model of your regular interactions based on e-mail conversations and group memberships, which it uses to organize people search results based on social distance - a direct colleague will appear before someone 3 degrees removed.

Index Partitioning:
SharePoint Search supports partitioning the index and having multiple indexers that can be aggregated together

Query Partitioning:

Each query partition can contain up to ~10 million items, and can also be “cloned” by deploying multiple instances of a given query partition across several query servers. Query throughput increases when you add query partition instances.

FAST Search replacement: The new architecture scales up to approximately 500 million items, and search can be utilized in a multi-tenant hosting environment.

Crawling Service:
Multiple crawlers can be used simultaneously to crawl different content during each crawl cycle. This improves performance and can also provide redundancy. All crawling information is stored into “property database”.
Cross-farm search service:
Cross-farm search service that allows farms to connect to multiple farms to consume cross-farm data

Metadata index is exposed via search.

People Search:
This functionality is available in SharePoint 2010 OOTB Search and Fast Search

Integration with BDC:
FAST Search
integrates with Microsoft Business Data Connectivity services in 2010 means that ingesting structured data from external Line of Business applications is much easier in FAST Search for SharePoint.

Cheers,
Kishore Kumar.N