The 1st difference, and arguably the most important one, is the image sensor's size. DSLR has an APS-C or Full-Frame (35mm) sizes CMOS sensors, where Powershots have much smaller, some CCD some CMOS sensors. this translates to superior image quality in terms of digital image noise - the larger the sensor, the less noise is apparent in the image. In this picture from Wikipedia, the 1/1.6" and smaller rectangles are the realm of P&S:
Also important is the fact that DSLR have interchangeable lenses, as well as TTL (Through The Lens) Optical Viewfinders which lets you see what the sensor sees.
DSLR are generally quicker than P&S, and occasionally have more features (but not necessarily, as the Powershot line has compatible CHDK alternative firmwares which enable many of the DSLR features).
Is it "enough"? This is a very subjective question. Given the price tag, the different size and weight group and more factors, only you can evaluate the "enough-ness" of a P&S camera to your needs.