I started using it early last year and then moved away from it after reading a couple of financial advice columns regarding how Canadian banks didn't approve of it or support it and could therefore disclaim all liability for fraud on the basis that you violated your banking agreement by giving out your password to a third party.
However, if you read the fine print on most of your banking agreements, [i]writing down your password{/i] -- and therefore by extension storing it in an app like 1Password -- is also
technically a violation of your agreement. Basically, if your online banking password or PIN is
anywhere other than in your head, the banks will happily wash their hands of any responsibility to you -- they're basically looking for excuses to do so, really
An acquaintance of mine had his debit card compromised and lost around $1,000 via three bank machine withdrawals. During the discussion when reporting it to the bank he was foolish enough to admit to that he kept his online banking password stored in a password-safe application on his PC (they didn't actually
ask the question -- the guy merely talks too much

). The app in question stored the password fully encrypted, and he also had his entire hard drive encrypted with PGP Whole Disk Encryption. The bank basically told him flat out that he violated the online access agreement and was SOL. When he asked how his online banking password had anything to do with his
debit card being used to withdraw money from a bank machine, the bank responded that it didn't matter -- he had violated his terms of the agreement and the bank no longer had any obligation to hold up to theirs.
On the other hand, it's now also worth noting that
some banks do approve of aggregation sites if and only if they provide
read-only access to data (which Mint.com does). I think RBC is in this category; I'm not sure about others.
So considering that, combined with the convenience of having Mint.com automatically handle everything as opposed to keeping iBank up to date manually, I decided to switch back to Mint a couple of months ago.
To be fair, I'm still not thrilled with the experience -- Mint tries to be too clever for it's own good when it comes to renaming and categorizing transactions automatically, so you'll still find yourself having to go through and check things occasionally to make sure they were correctly named and categorized. Further, any rules you configure on Mint.com are based on Mint's
renamed version of a transaction, as opposed to what your bank statement actually says, and auto-categorizations are keyword-based. For example, Mint tends to categorize purchases at Grand & Toy as "Toys" rather than "Business Supplies." Some of these can be overridden with your own rules for places you normally shop at, but you'll run into edge cases all the time. The more serious issue is when Mint decides to categorize multiple source transactions with its own single name. iTunes purchases are particularly egregious for this: Both "App Store" and "iTunes" purchases get categorized as "iTunes" even though the names on the statement are different, and there's no way to create a rule to separate these as rules are based on Mint's name, and not on the original name on the statement.
If you go to Mint's support site, you'll see numerous reports of the problem over the past couple of years with no indication that Mint is going to be fixing it any time soon. It doesn't have a huge impact on me as my transactions are dissimilar enough, but you'll see reports in the Mint support site from users who have much more serious problems with this due to things like working at a grocery store or gas station (all of their paycheques get assigned to"Groceries" or "Gas").