Online banking sucks
It's like banking in Europe 10 years ago. Think Internet Explorer. Think Javascript scripts timing out. Think Java. Think no way to report bugs. Think no acknowledgement of reported bugs. Think if they ever roll out an update to fix your issue, they break something else. True story.
I'm thinking of starting a blog highlighting the hilariously bad engineering going into Singapore made banking Web applications.
No super convenient ATM network
You have to learn where your bank's ATMs are to avoid charges. Good luck!
Domestic transfers take THREE DAYS
Transfer done before 12pm on day 1 will arrive either by 6pm on day 2 or 1pm on day 3. That's the one that costs no money. If you want a domestic same day transfer it costs $20 per transfer.
It's like going back to the pre-2008 in the UK. Without the 20SGD charge.
Interestingly the EU only recently regulated faster payments across Europe.
Using a debit card? That's 10% thanks!
There is a charge for using you card. For example it can be charged 10% if you hand over your card to the taxi driver.
One way to lessen the charge is to ask to pay by NETS, whereby you are only charged 30 cents. Compare that to Europe where debit cards incur no costs, so don't make assumptions.
Evidently merchants are confused whether you want to be charged by the more expensive direct debit or NETS. Ask for NETS, then the merchant will probably demand cash since remember it takes 3 days for them to get their money from NETS.
Confusion over bank codes
You might get a Bank code number like 7144 and a Branch code number like 057. These are used in transfers between Singapore and Malaysia typically.
Nonetheless the term Bank code is interchangeable with the SWIFT code, leading to a lot of confusion. Good luck paying your bills!
Don't change your mobile number
If you change your number in Singapore you might be in for a shock. Most security is tied to your telephone number and you have to at the very least go to a branch to get your number changed.
If you are abroad, you might have to do what I did. Email. Email again. Write a letter. Wait a month. Have bank staff tell your number is updated and still see the old number in the system. Go crazy. Go back to Singapore to go to a branch to update the number. Surprise!
Paypal UK != Paypal SG
That goes for banks too. If you think it's easier to move money around because you have a account with the same company in your country, don't.
For example if I want to move my company's UK subscribers to Singapore, I have to get each one to re-setup in Singapore. Ha ha ha, oh god no.
Charges are opaque
I received over 100SGD in charges on my account, which looked online like:
8163 05/12/2012 05/12/2012 Cash fees for: 0337322GR:1307
I emailed my banker asking what there were exactly. She said she won't know until the paper bill arrives. forehead slap
Good luck working out foreign payments
If you invoice clients abroad, you will need to wait an unpredictable amount of days until it arrives in your bank account.
Furthermore when the remittance arrives, you are left with the conundrum of working out who just paid you.
050IT13011500224 8835 16/01/2013 16/01/2013 050IT13011500224 1/GEMEINDE GROEB SGD 241.89CR
This was painstakingly worked out as a payment of 200USD from a Scottish customer. I.e. a very manual task.
No automation features with company back account
Want to complete standing order online? You can't. More manual work you need to account for.
Update: Charges are exorbitant
I've since found out the 100SGD charge above (charges are opaque) was for transferring money to a Malaysian account. I ticked the box to accept the charge for the receiver and charged (like a wounded rhino) 50SGD for sending and 50SGD for receiving. 100SGD is more than 50GBP, for something that I equated in my mind to be something like a EU money transfer.
100SGD to send money in "Malaya" is INSANE. I asked my accountant at Kolibri Solutions Pte Ltd and she said that's normal and what a lot of companies do instead is use remittance services. Remittance services which you need to attend in person at a counter in Clarke Quay area, where they charge something like 5SGD instead of the online bank's 100SGD to get your money transferred.
I'm shocked.

It's only very recently that bank transfers in the UK have become faster than three days, I'm talking like this year.
There is an argument I've heard that says that in the UK we fool ourselves into thinking that banking should be free. And once we think that it's free no one is going to pay for it. Which is why we end up with such huge charges for going overdrawn etc. You don't mention how much this costs in Singapore, maybe less? For example, ATMs, you think that banks can offer that service for nothing? Maybe in Singapore the charges are just more honest, you actually get charged for what costs the bank money.
Good comments Jamie.
I've asked the payments demi-god Dave Birch, and it looks like UK got fast around 2008. I've since updated the blog.