I found out that the MySQL 5.1 development source version has changed to 5.1.11, so MySQL 5.1.10 will probably be released very soon.
This is especially interesting for two reasons. First, MySQL 5.1.9 had a major bug in the Event scheduler, which will be fixed in 5.1.10:
"Executing a CREATE EVENT statement could cause 100% CPU usage. (Bug#19170)"
Second, MySQL 5.1.10 looks like the first full featured MySQL 5.1 version for Windows. It will include the CSV storage engine which will make it possible to write the general_log and slow_log into database tables:
"Logging to the mysql.general_log and mysql.slow_log tables did not work for Windows builds because the CSV storage engine was unavailable. The CSV engine now is enabled in Windows builds. (Bug#17368))"
Also the mysql_upgrade command will be available for Non-Unix-OS, too:
"The mysql_upgrade command has been converted from a shell script to a C program, so it is available on non-Unix systems such as Windows. This program should be run for each MySQL upgrade."
To see all the changes, take a look into the Change history. 5.1.10 really looks like a very interesting release.