Well I found the paper I've been using to track my improvement with my times, and this is how I've improved :
Got my cube on January 22, 2011.
First ever solve with instructions printed next to me - 6:48.71.
Next day, first ever solve without instructions - 4:20.63. By the end of that day I hit 2:23.53.
Next day - 1:59.66. Sub-2 minutes in 2 days!
After first week with cube, my best single solve was 1:31.45.
After 2nd week, 1:24.78. 2 days later I hit 1:08.93
After 3rd week, 58.22 seconds! I had subbed a minute with a Rubik's Storebought!
After a month with my cube, I had a PB of 44.15.
The first ever video taken of me cubing was 5 weeks after I had gotten it, and the time was 43.84

I started improving very quickly now, as on my 6th week my time was 32.85.
On my 8th week (literally no improvement on 7th), I had finally subbed 30 on my Rubik's Storebought with a time of 29.99! (LOL)
After that cube exploded beyond repair, my friend gave me a Transformers Storebought cube which he said he had lubed with VASELINE.
My first sub-20 came exactly 6 months after cubing, at 19 seconds flat.
Now, 2 weeks later, my full-step PB is 18.53 and my lucky PB is 13.09!
So I guess I improved extremely quickly at the beginning, only because I had practice nearly all day, every day. It took me 2 months to sub-30. After that it took me another 4 months to sub-20! I guess it's harder to improve once you hit 30. I've known full PLL for 3 months and know about half of the OLLs now. My F2L needs serious work. Perhaps if my dad would buy me a ZhanChi and I could stop using this Vaselined-Tranformers-Cube, my times would be a bit better?
This was just my improvement, and a bit of me rambling at the end.