I've solved 273 as of now (https://projecteuler.net/profile/NabiNaga.png). It took me a little less than 2 years to get to 250 problems, but I was spending quite a bit of time on them haha. I've learned an incredible amount of math and algorithm skills from PE. There have been lots of really challenging ones, but one that stands out is 494. That was the first "really hard" one I solved, and my first time to be in the first 50 solvers.