Seems like a good place for a first post as any... I've been using mulch for several years now. I'm still using version 1, as I like the interface more -- it's not as slick, but I find it generally easier to use, plus it's more friendly for small screens. The relatively recent 2.1 release that has custom time signatures etc. is quite an improvement, but I can't afford the upgrade now anyhow :p.
I found it extremely easy to get into, but yet it has a surprising amount of depth. Even after all these years I am still learning new tricks with it. At one point I'd thought of starting a mulch-tips blog but I stopped making music at all for a while, and these days there's no time.
Well, I'm definitely having fun with it! 
1st patch results - http://soundcloud.com/leberger/new-toys
Nice 1st composition!
My initial hang ups with it is the (seeming) lack of editing tools to work straight up with waveform / samples, the lack of precision with certain tools (like the harmonizer, can't enter a value, you have to scroll the mouse on the fader and it's not too precise) and choice of effects (where's my convolution reverb?! My pitch shifter?|?|?|?)
Most items you can edit the values of by right-clicking. A few things like the harmonic weights on the Shaper can't (don't know if this is what you meant by harmonizer) which is unfortunate. If you
need precision on these things, and you don't need to adjust it in real-time, Audiomulch saves its files in XML format, so you can load them into a text editor and enter numbers that way. A bit hacky, but it works.
As far as lack of effects, VSTs are a big help in making things more flexible. Mulch's interface makes it nice as even a pure VST host. You can also do a lot with the included devices when you start combining them, but this makes more sense for some things than others -- you can get some different reverb characteristics, but you're not going to get anything like convolution, for instance.
