松信です。

MySQL 6.0系の最新のアルファ版となる6.0.4がリリースされました。
http://dev.mysql.com/downloads/mysql/6.0.html

このバージョンからは、かねてからの懸念事項であった、
UTF-8の4バイト文字対応(サロゲートペアの対応)が実装されました。
※当初バージョン5.2という計画があったのですが、5.2そのものが無くなり、5.1→
6.0というリリース順序になりました。

基本的には、以前本ML([mysql 13823])で挙げた、
> 3.現行エンコーディングutf8(3バイト)の名称をutf8_oldに変更する。そして
> UTF-8 4バイト対応のエンコーディングutf8を追加する。(残るのはutf8_oldと新
> utf8)
が採用されました(utf8mb3とutf8)。
森山さんはじめ、当時フィードバックをくださった方々に感謝しています。

具体的な使い方については、近いうちにどこかに解説を書こうと思っています。
興味のある方はぜひ試してみてください。
また、仕様等が納得いかないと思われた方はご連絡ください。
(アルファ版の段階であればある程度の修正も可能なので)
バグを発見された場合バグレポートに投稿してくださると非常に助かります。


---(以下リリースノートから当該部分を抜粋)
* Incompatible Change: The Unicode implementation has been
   extended to provide support for supplementary characters that
   lie outside the Basic Multilingual Plane (BMP). Noteworthy
   features:
   + utf16 and utf32 character sets have been added. These correspond to
     the UTF-16 and UTF-32 encodings of the Unicode character set, and
     they both support supplementary characters.
   + The utf8 character set from previous versions of MySQL
     has been renamed to utf8mb3, to reflect that its encoding
     uses a maximum of three bytes for multi-byte characters.
     (Old tables that previously used utf8 will be reported as
     using utf8mb3 after an in-place upgrade to MySQL 6.0, but
     otherwise work as before.)
   + The new utf8 character set in MySQL 6.0 is similar to
     utf8mb3, but its encoding allows up to four bytes per
     character to enable support for supplementary characters.
   + The ucs2 character set is essentially unchanged except
     for the inclusion of some newer BMP characters.
   In most respects, upgrading from MySQL 5.1 to 6.0 should
   present few problems with regard to Unicode usage, although
   there are some potential areas of incompatibility. Some
   examples:
   + For the variable-length character data types (VARCHAR and
     the TEXT types), the maximum length in characters for
     utf8 columns is less in MySQL 6.0 than previously.
   + For all character data types (CHAR, VARCHAR, and the TEXT
     types), the maximum number of characters for utf8 columns
     that can be indexed is less in MySQL 6.0 than previously.
   Consequently, if you want to upgrade tables from the old utf8
   (now utf8mb3) to the current utf8, it may be necessary to
   change some column or index definitions.
   For additional details about the new Unicode character sets
   and potential incompatibilities, see Section 9.1.8, "Unicode
   Support," and Section 9.1.9, "Upgrading from Previous to
   Current Unicode Support."
   If you use events, a known issue is that if you upgrade from
   MySQL 5.1 to 6.0.4, the event scheduler will not work, even
   after you run mysql_upgrade. (This is an issue only for an
   upgrade, not for a new installation of MySQL 6.0.4.) To work
   around this upgrading problem, use these instructions:
   1. In MySQL 5.1, before upgrading, create a dump file
      containing your mysql.event table:
shell> mysqldump -uroot -p mysql event > event.sql
   2. Stop the server, upgrade to MySQL 6.0, and start the server.
   3. Recreate the mysql.event table using the dump file:
shell> mysql -uroot -p mysql < event.sql
   4. Run mysql_upgrade to upgrade the other system tables in
      the mysql database:
shell> mysql_upgrade -uroot -p
   5. Restart the server. The event scheduler should run normally.
---

以上です。
----
Yoshinori Matsunobu
Senior Consultant
MySQL, http://www.mysql.com

MySQL Consulting Services:
http://www-jp.mysql.com/consulting/