I downloaded Soulver to see whether it would be useful for my kids to do their Maths homework. For primary/mid school students, I can say this is a *fantastic* application. It looks excellent for upper school, but haven't seen it used there.
Soulver has a very simple interface - if you just open it and type (e.g. 2+2) you see the answer immediately - very intuitive.
The big advantage Soulver has is that it lets the student show each stage of solving a problem. Homework assignments are done completely in Soulver - type a heading/date/name, type question numbers, and then type expressions/equations and results.
Soulver lets you combine lines of text and numbers, while easily resolve the value of expressions. So an algebra problem might go:
Q2. Solve 4a -2b where a=4 and b = 3
4a - 2b
=(4x4)-(2x3) (Soulver shows answer as 10)
For younger maths students doing homework, this is invaluable.
Soulver lets you easily enter mathematical symbols (divide, square root) as part of equations.
I compared Soulver to MathPad. For some inexplicable reason, MathPad seems to think that showing the working out for long division and long multiplication is vitally important. News for MathPad - it isn't. Mathematics teachers have moved on, and nowadays its perfectly acceptable to calculate 625/25 with a calculator, rather than having to work it out the long way. The US assocation of mathematics teachers is very clear on this, as are other mathematics bodies.
The Soulver approach is to provide a clean worksheet enviroment for kids to work in. They can do all their homework assignment and then print-PDF-mail it to their teacher or print it out and hand it in.
If you have kids at school, download the software and try it. It all just works.