I bought my 400D in April 2007, and although I enjoyed it a lot, I realised that the 18-55 kit lens wasn't long enough; I had to invest in extra glass.
I considered, then dismissed, the 28-135, on the grounds that it would turn the camera into a glorified superzoom. So, 75-300 f/3.5-5.6 IS, or 70-200 f/4L? Every comparative review and every Canon user I spoke to recommended the L-series, despite the apparent limitations of a lack of IS and a shorter focal range, and at the end of June, two months into DSLR ownership, I put my money down for one. No regrets; it's been an outstanding bargain, orders of magnitude better than the "thrifty fifty" 50mm f/1.8 I purchased at the same time, or the supplied kit lens.
Still, for wide-angle shots I could still rely on the 18-55. Look at the detail I was able to capture after only a week with the camera. And at the end of June, my front page scoop photo was taken with the kit lens too. That's why I haven't bought any new glass since last year.
More recently though, I've been trying my hand at a few different types of shots, and one of the ones I want to try is portraiture. I felt the time had come to upgrade, but what to choose? The two standout candidates were the 24-70 f/2.8L, and the 24-105 f/4L IS. The 24-70 was by all accounts the better lens, but it was only on full-frame bodies that you could really tell the difference. Also, while it was faster, it didn't have three stops worth of IS to offer, and if I needed speed that badly, I had the 50 f/1.8 to fall back on. The 24-105 was lighter, cheaper, more discreet, and offered a better range for a walkabout lens. So...
...I bought a 24-70. Huh?!?
I thought I was committed to the cheaper lens, but a bargain appeared on eBay, and I got a bit trigger-happy. I'm still not convinced I did the "right" thing, especially given the weight of the beast, but hopefully I can put it to work earning its keep. It's by some margin the most expensive photographic kit I've ever bought (and that includes the body of the 400D itself), so I'm determined to make the most of it.