MyISAM or InnoDB

What’s the deal with MyISAM vs. InnoDB for Rails? Here’s what I know and think I know so far:

Reasons to use MyISAM:

• Faster according to anecdotal evidence. But is that really true, and how much does it matter given other factors?
• Easy backups are easy with mysqlhotcopy
• Full-text indexing

Reasons to use InnoDB:

• Transactions
• Foregin keys
• Row-level locking
• Rails defaults to InnoDB when creating new tables
• You can delete your Rails sessions in one go without locking the whole damn sessions table

I’m leaning towards using InnoDB, because:

• It’s the default for Rails so I don’t have to work around it
• It has more granular locking, which is good if you plan on getting lots of traffic
• It has transactions, which is always healthy
• You can do backups using mysqldump, which is OK
• You can do your searches with Ferret, which is much better than the MySQL full text index, anyway
• You can delete your Rails sessions in one go without locking the whole damn sessions table

Is there an official recommendation? What do some of the big-site folks out there do?