It will depend on the price really, and whether the camera is what you're after. That is to say, bear in mind that digital SLRs are a lot like computers, there is a certain amount of technical advancement with each new generation therefore I would expect to pay significantly less for a camera that isn't current technology. Then you also throw in standard depreciation for an item that is fairly complicated both electronically and mechanically, and you would expect to pay even less.
Unfortunately as has been debated here before, second hand prices in Singapore seem extremely high in general, but that doesn't mean you might not be able to find a good deal somewhere, and if so then yes, assuming you check the camera out as thoroughly as you can (bring a *properly* experienced friend along to check) then they're worth buying.
The key really is the price, and saving 20% on anything that is second hand and not in warranty (I think most manufacturers' warranties are not technically transferable) is the bare minimum you'd expect to get off, and more if the camera has any sort of age. If it's not current generation then I'd really expect a sizeable discount.
Going on the prices others have posted, no. Not by a long way ^.^
I've used this example before but over here in the UK I paid the equivalent of S$2068 for a one week old S$2951 lens. As a very rough approximation that would be something along the lines of S$1100 for a S$1600 camera.
I'd be amazed if you get anything like that sort of price in Singapore, but really you'd expect to get more than S$150 off. As others have mentioned, warranty, peace of mind, and a kit that is fresh from the factory.
1. buy TWO generations back (out of warranty) and avoid stuff that has JUST gone off the shelves.... my (flawed) logic is simple: if its lived this long, it should last a few more good years
2. No assurance but generally prefer to buy off amatures and/or newbies infected with BBB virus who generally tend to really baby their equiptment
3. Try non-C and non-N other brands like Oly, Pana , etc etc
4. Avoid buying from people like Jed and ditto, who tend to send their equiptment to Hell and back .... several times (just kidding ha ha )
5. TRY to buy from someone I know personally
New or 2nd hand ....... my pics are not going to come out different better/worse
Personally I tend to stick to one generation back because  at the moment two generations back is still weak technologically and  you should be able to get good prices on one generation old cameras. Maybe not in Singapore which is why Ed suggests two
Agree very strongly with his second point though Although the odds of someone qualifying under point 2 and still having their two generations old camera is quite low given they tend to sell the moment something new comes out
TS seemed to have lumped DSLR and lenses together. Here's my assessment on these 2 separately...
My few lenses and my body are all second hand stuff.
Items devalue immediately once it changes hands the first time, for lenses that would probably be around 15-20% off the current retail price. The good news is they're unlikely to depreceated further unless a better version of the lens is produced. That means that when you decide to change lenses at any time, you won't lose a single dollar and might easily turn a small profit if market conditions swing your way.
As for bodies, it really depends, I won't buy anything out of warranty because I want to send in for general maintenance and cleaning the moment I get it and I don't want to pay for that if its out of warranty. Its also hard to test a body comprehensively on the spot and it would be helpful if there are any hidden problems. The price for last gen bodies is generally ALOT lower, in the region of 30% or so, so if you don't mind *slightly* older technology, then its a good bet. Also you'll ocassionally find sellers who bought extended warranty for their other bodies - which generally cost them quite abit - it can be a really good deal when they sell low enough to match prices of other used bodies without extended warranty.
Finally, don't worry about shuttercount. Most cameras are now rated for 100k++ and unless you're into sports photography, it would be a tough number to hit. Say you were to use the camera every other day for the next 2 years, that's 250+ shots every time you bring your camera out. And even then its not guaranteed to fail.