Well a question you have to ask yourself is why the seller is selling a Late 2011 machine that's only a year old?
Since the warranty runs out in a year, and they didn't purchase AppleCare, is it possible it has a hardware problem and they are looking to dump it on some unsuspecting bloke?
I'll need to use this with applications like Adobe Creative Suite 5.5
Well if the machine has 10.7 on it, it should run CS 5.5 fine, but if it has 10.8 on it then you need CS 6
Does this laptop have the muscle to handle these apps...
Oh sure, no sweat. You might want to increase the RAM to 2-8GB 204-pin PC-10600 (1333 MHz) DDR3 SO-DIMM
...or should I be looking at a new system with better hardware like USB 3.0?
That depends how often your accessing others external drives and what type, it does have Thunderbolt though.
If so, what would you recommend? BTW, I usually own laptops for 3-4 years before upgrading.
I don't think it's a bad choice of hardware, being it's only a year old. But it does make me suspicious why they would want to give it up so soon.
Usually people dump their Mac's about 3 year point, not one year. So you will have to ask a few questions in a way that they won't lie to you about the real reason.
If it has AppleCare on it and you check and that hasn't been violated (like the user dropped it or spilt water inside setting off the sensors) then it might be a decent buy.
There are plenty of reasons why someone would sell such a new computer. The original poster mentioned one (change to a smaller system). There's also the desire to upgrade to the latest and greatest. Maybe the person selling lost a job or had some unexpected bills and needs the money to pay them. Perhaps they realized a Mac was not for them and wanted to go back to Windows. I could go on, but suffice it to say, it's more than likely not a nefarious one. Besides, if there were something wrong, why wouldn't you try to get it fixed if you're still under warranty?
I had an early-2011 MBP that I bought brand new but sold about 6 months later because I got a phenomenal price on a brand new late-2011 model; the upgrade bascially cost me the equivalent of a bit more than the sales tax.
In any case, OP, I second CMCSK's advice. Make sure you can examine the system before you purchase it. Now if they try to resist or deny you that request, walk away. If they're open, I see no reason why you should not proceed with the deal.
If yoi don't have any peripherals and are going to start investing in such, 3.0 is the sensible option. However, some of us oldtimers have a significant investment in gear and the former way to get fast I/O was using FireWire, which the 2011 models are the last to carry native interfaces. OTOH, Thunderbolt is the great unfulfilled promise; does blow the socks off anything else, but its still closed and proprietary nature is seriously hampering its adoption. Heck, a friggin male to male cable costs over $50 and has to have the Apple moniker stamped on.
As for testing, bare minimum is that the Mac pass an extended Apple Hardware Test: http://support.apple.com/kb/HT1509