I don't want to slag Modo off, as I'm a luxology fan and own and update Modo, even though I rarely use it.
Before switching to Arnold, I was using Modo for a while and got used to its rendering workflow, which I found to be far more fun than Mental ray, but nowhere near Arnold, hence the switch.
However, my general testing drove me to the conclusion that modo is not even in the same country let alone the same ball park as XSI and the reasons are too many to mention and permeate across the board. It's very slow in general, cannot handle even medium data sets very well, soon becomes cluttered with poor scene management. (Still seems very modeller first and foremost- renderer second )and has too many hoops to jump through to do simple things like link parameter together. It's just way too simplistic for anyone who rigs to more than a basic level. IMO. They have gone for ease of use rather than depth, and yet still can't match XSI, in elegance, ease, or depth.
Bring ICE into the mix and the separation becomes extremely profound. It's like comparing a Porsche to a pedal car.
However, I like luxologys communication and respect for its userbase and I think they do a really good job with updates. Modo, is still embryonic as a TD tool so who knows how it will develop?
They need to gigapoly modo and give it nodal low level access if they want to compete with the big boys in the TD dept. I suspect however that they are going for a different market than the high end.

Agree with Mr Pooby, as price tag suggest, modo is not aimed to big studio but to freelancer and small studio (but is used in some big production like Rage).

What I like in modo is the idea of doing all in a single package. Its sculpt cannot be compared to zbrush, modo paint 3d can be compared to Mari and rendering is not Arnold, bun in modo, without leave the application, with the some shortcut, paradigms and rules, can sculpt and adding a edge loop at fly where I need, or poly modelling and using some brush for push or add volume to my mesh; some for paint, can paint in 3d, find an error on my uvmap (unwrap in modo is IMO more advanced compared to XSI) correct it and work without issue ect. all without leave the application, whitout import/export errors issue. For me a big step forward in my workflow, now leave a software for doing something in another application remind me the worse Lightwave workflow...

Rendering is really fast and simple, no issue with it, I think they want a system more useful and power possible without issue, very friendly. Preview window is really nice, can paint a texture and control in a fly how its work with my material.

Agree when Mathaeus said XSI workflow is more advaced, fast and efficient in modelling and rigging, but, if we excluding rigging (the most new part in modo), all modo is customizable, like GUI. My idea of gui is softimage, but if I want I can cage modo gui in a softimage like, some for modelling tools, modo can combine tools in pipeline tab, not a power solution like modo ICE modelling, but work fast and efficient, also can simple customize the basic tools (right click on pipeline when a tool is active, and select how the toll must work when you active it). When customize modo tools modelling become very fast. I also like blender 2.5/2.6 gui, cannot understood why people found it so complex

I'll expect a streamline process in 701.

Respect to Luxology, they doing all in house, from modelling tool to rendering engine (if we excluding Ikimena, all the software done by luxology hands)
Hope they will doing better and better, is good have some concurrent software, so AD are not alone

man this trial is crashy...

There are some things that I plain dont like at all about modo though after singing its praises.
First off is the material editor , which is god-damned ass backward as f**k.Layer based with masks...seems very unintuitive to me ,after getting used to node based systems its nowhere near as good as Softimage.......but then no other 3D package is ,is it
Also baking out textures for the edge padding to work you have to add in a separate alpha writer node.
The new character skinning is really slow to paint weights....I mean REALLY slow plus there is no weight table to fine tweak stuff.
There is no visual cue for open edges so you just have to turn on subd smooth and hunt around for something that doesn't look right.
On the modeling side ,although the tools are pretty good ,there are some problems that seem to be at the core of the modeler.One of them is when you cap a hole and it creates the polys with the normals flipped...dont know why it should do that .Also there are times when the viewport renderer doesn't draw polys in some situations.They pop back when you add a vert or generally change the topology.
I feel its a good software for a one man shop ,which is what I bought it for as Im making games with unity .But for it to even come up to the shoulders of the big 3 its gonna take at least 3 years of feature additions and code polish.

So which is it? I am confused...
(and yes, I will try it myself soon, but really would like to know what I'm in for)

Now on my machine don't crash at all, cannot say about others experience.

Agree with Manticor, is evident Modo has some issue in workflow (is young) and little things here and there (i.e. modo cannot export single obj object, but export all the object in your scene

SP2 is around from a month now. Must say is pretty solid (the list of fix is very long), also they add many improvement: e.g. now can handle more heavy scene (not like softimage, gygapolygons is unbeatable)

Also, CMIVFX release a nice rigging tutorial, must say rigging in modo is better than my previous experience without tutorial:
http://www.cmivfx.com/tutorials/view/483/Luxology+Modo+Character+Rigging+V1

and Richard Yot paint tutorial reinforce my idea about the good paint capabilities modo have (IMHO better than zbruch) :
http://www.luxology.com/store/texture_painting/