I use gmail as my primary email client because it’s quick and also I can access it from anywhere.  But there are some really annoying things about it, and I will gripe about them now.

• It is impossible to write filters that would help reduce spam levels.  For example, any mail that arrives with asian or cyrillic characters in the “from” column is going to be spam, and I’d like to delete that straight off.
• Deleting large volumes of stored mail at once is near impossible.  I have mailing lists with over ten thousand messages in them, but I can’t bulk delete them and if I want to I’d have to page through them 100 entries at a time.
• Lots of my friends have multiple email addresses, but they all count as different entires in the address book.  It would be super if I could select four email addresses and hit “merge” so that they would all be joined in some super-contact so I don’t get 200 duplicate suggest every time I start writing an email address starting with “joh..”
• If you have a contact with multiple email addresses (which you manually entered), it will still suggest their @gmail address even if you set their primary address to a different one.
• The calendar is poorly intergrated, and the reminder email doesn’t always work as I discovered yesterday.
• The conversation threading feature is very cool. but when its not it can be very annoying.  Especially in a >2 person email conversation, it always lists the first person to send the message at the front of the message even if someone else replied last.  Example: wordpress comments notifications.
• When I click on a “mailto” link on my desktop, that doesn’t bring up gmail.  I could probably hack a workaround for this though.
• Probably more. It’s still a great system, and I’m going to keep using it — but I wish it were better.