Don't assume you know everything before you post.

I have searched the market, and used K-9, and since K-9 is based on the same architecture as the default email application, it is borked in the same way. Yes, K-9 does have options for syncing, and very nice they look to. But you clearly haven't used them in anger, because if you had you would realise that a connection failure makes the application think 'oh all your mail has disappeared' and you then have to do a complete re-sync. Even opening emails is a 'trick too much' for the built in IMAP client some times - quite a lot of emails opened just show 'connection error'. What that actually means is 'the IMAP classes have thrown an exception, the details of which you can see in the k9errors folder, but I'm just going to say connection error because then it looks like it's not the applications' fault.'

I am not alone:

http://gizmodo.com/5068743/t+mobile-g1s-pop3imap-email-is-down
http://androidforums.com/t-mobile-g1/1400-g1-email-imap-issues.html
http://forum.androidcentral.com/t-mobile-g1/15-pop-imap-client-broken.html
http://modmygphone.com/forums/showthread.php?t=5461

You're not sure why i'd use an IMAP client when the gmail client is right there. Perhaps this is because I have my own IMAP server, where I keep all my mail? Maybe I don't *want* to switch to GMail right now?

So, I repeat your comment, mostly:
Either search the market more thoroughly or take the time to see what the application has available before you slap-down. Had you done the first you would realise K-9 is currently the only viable alternative, and had you done the second, you would have realised that it's rubbish.

What are you on about? K-9 email works quite well with imap, pop and even webdav (though not as well as imap). Folder classification allows for displaying/syncing only the folder you want, it supports downloading attachments and it's free.

Gmail IMAP support works well because they take the time to explain all the appropriate settings and have a stable server (tho I'm not sure why you'd use IMAP when the gmail client is right there).

Either search the market more thoroughly or take the time to see what the application has available before you complain.

...that 'Non-GMail IMAP Support that isn't complete pants' isn't a new feature.

I hope somebody creates a decent IMAP client support soon - I'm not a fan of having to download the entire mailbox every time I open it, nor of being told that all my folders are empty just because the phone can't manage to connect to the server.