Well, on 3G it took approx 1 minute for my email to popup on my phone, with the screen off. Not the longest amount of time, but I guess if you absolutely must have it instant =/ I dunno. Haven't found a way to make it constantly poll for new emails.
Yeah the update every 30min option on email sucks I want to check every 5min at least on my phone.. My Storm did receive emails really fast on my work email but hopefully things will change
Not enough in this discussion to know what email server you're all talking about, but with my company's IMAP server I receive my email instantaneously using IMAP idle (literally within 3-5 seconds after successfully sending). Gmail comes in usually under a minute (also IMAP). I use K-9 for my mail client.
Whoops it's 15min is the lowest setting for what I have my "Fetch Schedule"
I setup a POP3 Email account for work since I use a hosting company. If you open up your email and hit the 4 Square button then --> Email Settings --> Email Delivery --> Fetch Schedule.
I don't have an option for Data push on the server I have so I have to fetch and 15min still sucks IMHO