My E520 came with a 17.5-45mm `special' kit lens and it did its job whilst I was leaning to get to grips with the camera, but, as with all kit lenses, it's limited with what it can do so I knew I had to get a couple of extra pieces of glass, one of which was the 70-300mm. Though I'm not in a position to compare this with other telephoto zooms, having used it for a while, I can tell you that it does take some great photos and with the focal length doubled on Olympus cameras, you can get `right in there'. It also shoots down to 38 inches in manual mode or 48 inches when auto is selected.
What you have to bear in mind is that although the physical size isn't great and the 22 ounce weight (that's 615 g) may not sound a lot, when used at the top end, it'll soon begin to get heavy after a while, which is why a tripod is essential. Something else you need to know is that if the camera is set to 'Manual Focus', the AF/MF switch will always operate in manual mode irrespective of what position the switch is in. Ah, the manual focusing ring. Why do they always make it as small as possible? One minor complaint I have is that when manual focussing, the ring seems to grind slightly at times, though it might be my particular lens but I can live with it.
At f4.0, this isn't the quickest lens you can get but is good for the current price. It closes down to f22. The thread size is 58mm and the package includes a hood. If you want something that takes nice pictures with good colours and is easy to get on with (once you've resolved the weight issue), you can't go wrong with this lens.