I used my 400D with just the kit lens for about two months, but I really needed a longer lens. At first I thought of the 28-135, but didn't want to use the camera like a glorified superzoom, so pretty soon I'd narrowed it down to one of two lenses in the £300-400 range: the 70-300mm f/4-5.6 IS, or the 70-200mm f/4L USM.
My mind was made up pretty quickly. The 70-300 offered an extra 100mm of zoom and three-stop IS, so on paper it had a lot to offer. But everyone was telling me the same: go for the L-series. Canon owners I knew raved about it, while many online reviewers concurred (e.g. The Digital Picture, Fred Miranda). The 200-300mm range of the longer lens was known to be softer, while the L-series had a fantastic rep for quality and sharpness. I went for a 70-200, along with a wee thrifty fifty prime (f/1.8).
It took a couple of weeks before I got a good opportunity to stretch the new telephoto zoom. I eventually took a trip up to Oban for a sealboat ride. I'd been on them before and they're very relaxing and enjoyable. I also had a chat with a pro photographer who had a stall set up near the harbour, selling his wildlife pics. And I finished with a fish supper from the Rick Stein-recommended Oban Fish & Chip Restaurant. The Anstruther Fish Bar might win more awards, but the chippy in Oban kicks its ass. G has spoken.