It's pretty enough in its own way, but do you know what my first reaction was? I first viewed your site in Chrome, then loaded it up in Firefox, and finally IE because I was convinced that something wasn't rendering correctly.

Two things stand out in particular: first, my laptop's resolution is 1600x900 and I have to scroll down to see the links on the left; secondly, that's a HUGE amount of empty space on the right hand side, and it looks like it could accommodate the "What is Simplton" text quite nicely.

Honestly, I'd advise doing what I do - although I'm not terribly successful, so perhaps you should disregard this advice ;-) Anyway, go to ThemeForest, find a decent sales page theme, and another one for your user area. It'll cost you $30-40, and whilst some will object to what are pretty obviously cookie-cutter themes, you'll find out pretty quickly if people will pay for it.

I was in the same place as you a year ago, with a tool whose design was 100 times worse than yours is, and I was signing up 1 trial account per day. Many months later I bought a design for $15 and an admin theme for $20, and that increased free trials to 20 a day!

Good luck! :)