Paul,
OSE is no-where near as complex as Google's algorithms and can only rank links in a relatively simplistic manner. Although it's a very good tool for getting an idea of what's going on, there are so many other contributing factors that Google will use that just can't be included in OSE.
For example, the directory links may be ranked highly in OSE because it's algorithm looks at all the links going into the directory and determines that it's probably quite a good source. Google however may have penalised the same directory (something OSE can't determine) and so any links from that directory may in-fact be worthless.
When using OSE, I tend to use my gut instinct as well as the stats to tell whether a link is worth anything or not. If a link looks particularly spammy then it probably looks the same in Google's eyes.
Also - it's worth remembering that OSE's index is much smaller than Google's, therefore although most of the decent links will be in there you may not be able to see some awesome links that your competitor has, simply because they're not in the OSE index yet.