I've always liked 150s. Fairly light weight and plenty of power for a smaller saw. Problems areas that come to mind are:
1. The clutch covers tend to break easily if banged around at all.
2. The fuel tank is integral with the rear handle assembly and is not meant to be split. If it ever starts leaking, it can be a bit of a job to repair it properly.
3. Engine removal is fairly easy, but the carb linkages can be a bit tricky if you've never worked with one before.
4. Uses a special rotor not instead of starter pawls for cranking. I haven't had one fail yet, but these were a bit expensive last time I checked and may not be available anymore.
With these things mentioned, again, please don't take me wrong as I love the 150s. Anytime I need something a bit more than a Super 2, I usually grab a 150, even before I would a Super EZ. There's something about the feel and balance that just fits right. I agree with Mark, if its in very nice shape for $50 or so, then its a great deal. If it needs some work and its $20 or so, its still a good deal.
Dan