First of all, it's a very good idea to get the water away from the house; in general you don't want any pooling or draining water around your foundation. The farther away you have sump pumps, eaves troughs, etc going, the better.
You'll want to check the total discharge head of the pump before you do this. Pump performance is rated in terms of both volume (eg, gpm) and pressure (measured as head). The higher the head, the lower the volume. If you're already at the limit of the pump, then there is a danger it will no longer keep up with incoming water.
The head is a measure of the static discharge head (vertical distance between the liquid level and the discharge outlet) plus friction loss from the pipe itself. There should be at the least a rating for your pump model, and often there are curves that show the flow rates for different amounts of head.
I'd actually suggest avoiding that problem, and instead, running a drainage pipe (eg, 6" big-O) from your house to the back of your property. You'd then just have the existing PVC drain into that (with an air gap, to prevent water from being siphoned back inside). Be sure to slope the line towards the back of course so it does drain properly.
You could certainly perforate the lower section of the sump basin with small holes (1/4 inch/6mm or less would be my preference, but some might go twice/3 times as large - depends in part what you are bedding it in)
Outside the basin, you'd want washed stone (depending on soil type, possibly filter fabric and washed stone)
Inside the basin, a concrete paver is a suitable pump support. Don't put anything else in there that would make cleaning more difficult.
In my personal experience, pick a submersible sump pump - all the ones I've met have been much more reliable than the pedestal style pumps. To get the most out of whatever pump you buy, don't cheap out on the pipe size - plastic pipe is cheap, no good reason to reduce 2 inch threads to 1-1/2 inch pipe, but I see it all the time - even 1 inch pipe; don't do that - stick with whatever size the outlet on the pump is for best efficiency. And make sure it discharges far enough away from the building - I've met quite a few that pump the same water in circles, from inside to outside, where it comes back inside, to be pumped back outside...
Also, run the pipe straight up as high as it needs to go from the pump, then slope it towards the drain at 1/16 to 1/8 of an inch per foot (or 10mm per meter.)
If you are concerned about pumping rate, you can either try to come up with some sort of test flow (difficult unless the weather cooperates) or simply mount the pump to one side, so that you can add a second pump a few inches higher (use two pavers) if the first proves inadequate when the rains come. If you already have a pump in the old sump, start with that and see how it does.
Best Answer
Unless you have reason to believe that the sump output is contaminated, and assuming that you have legal access to the pond, this is a perfectly viable solution. In fact, even if the pond does eventually (or occasionally) drain into a stream, the natural filtering effect of the process should remain somewhat intact.
As Tester101 points out, local and state laws may apply. In my experience there's no problem ejecting groundwater into a wetland in a non-destructive manner. We've run open-loop geothermal systems into adjacent wetlands, and in Minnesota wetlands are strictly protected.