Keeping all your BTC on an online wallet seems to me like it could be risky. It is certainly possible for any of those services to go down, be hacked, or otherwise compromised. Read around a bit, MtGox has been hacked before (the exchange part it looked like), and other online wallet services have been hacked and had wallet info/BTC stolen.
I think following the advice in the 100% secure wallet thread is very wise: keep the BTC you are using in a public wallet, and transfer out amounts you are not going to use. As an analogy:
You might use a checking account for your weekly/monthly bills, but the bulk of your money goes into savings/IRA/portfolio to earn interest, because it would be foolish for that money to just be sitting in your checking account doing nothing.
For BTC, think of the online wallet as your checking account, and offline wallet as savings. However the bulk savings isn't moved for interest purposes, but for security purposes.
You don't need to even access the offline wallet to deposit BTC into it, or to even see how many BTC are in there, you only need to access your offline wallet to take out your BTC, and that should not be very often at all.