Had evaluated mysql 5.1 and found it to be very good.
Check this out
[root@localhost mysql5]# ./bin/mysqladmin -u root -pjayant status
Uptime: 38621 Threads: 2 Questions: 98346998 Slow queries: 0 Opens: 0 Flush tables: 1 Open tables: 119 Queries per second avg: 2546.464
The no of queries/second is very high. And the load on the machine is around 2.
Have tried out mysql partitioning on one of the tables. The table has large no of rows - around 90,000,000. And the results were very good. I was able to get large no of queries serverd at the same time from the table.
Few more improvements in the partitioning algorithm can make it rock.
1. Parallel execution of queries on all partitions
2. More efficient administrative commands like alter, add, COALESCE partitions.
3. Decrease locking time of partitions not required in a query.
4. Provision to lock a partition without affecting other partitions.
For more information on partitioning pls go thru the following blog
Hope mysql 5.1 works out fine...