I bought this great little lens 18 months ago from Calumet to stick on the front of my EOS 400d. I'm very pleased with my purchase, not least because it cost me £125. At the time there was a suggestion that Canon and Nikon were on the cusp of raising their prices - fast forward and the price has roughly doubled - at the time this lens was less than twice the cost of the EF 50mm 1.8, it's now considerably more than that...
So, why has it gone up in price so fast (and apparently risen faster than other Canon lenses)? Possibly it's just a case of demand - you get a tough, well put together lens with a focal length which mimics a 50mm standard on a 35mm camera. You get usably sharp images across the frame when open to f2, so you can use it inside without flash, and unlike the 50mm 1.8, you can take a picture inside in a normal sized room without being limited to head and shoulder shots. Some users have complained about the bokeh not being perfectly smooth - well it isn't a £1,000 lens, but anyway it looks great to me.
All in all I'm very pleased with the lens. At the price I paid (at the cheap end of high st at the time), it was a bargain. Would I buy it for £250 plus? I'm not sure. I might find myself looking back at the EF 50mm 1.8 (at around £90 with it's a faster lens with superior sharpness), or saving up for something more high end(the EF 28mm 1.8 maybe).
For all of that, if you pick this lens up I'd be very surprised if it didn't become your new favourite - it's very nice.