I just tried it. Quite interesting.
Pros:
1) fairly modern but minimalist UI;
2) auto-detects winavr - zero configuration on my part;
3) extensive built-in drivers for avr/lgt - beats out arduino;
4) highly integrated: from device configuration, editing, build to program, all in one;
5) small download (just over 2MB + .net). No installation required.
...
Cons:
1) resizing of windows not quite working;
2) limited support: two devices (lgt8f88 / atmega88 and one other).