With version 5.1.7, MySQL 5.1 (which is something I'm [not] patiently waiting for) has gone from alpha to beta status.

The stuff I'm really looking forward to is it's improvements to the NDB Cluster engine...

• Disk Data tables (before NDB Cluster required everything to be memory-resident)
• Integration of MySQL Cluster and MySQL replication
• Variable sized records

Now hurry up through the beta phases!

The only thing (that I can think of) that MySQL Cluster will be lacking for 5.1 is support for FULLTEXT indexes... not a deal breaker though since you will be able to replicate to a MyISAM to get a FULLTEXT indexed table. Should see it in MySQL 5.2 though (hopefully). Oh, and the ability to alter live tables sure would be nice.