Probable penalty?

[milez]

Hello WW.
We are in the process of setting up a portal in a very highly-contested category.

In the last update we recieved PR5 and have about 200 backwards links of PR4+ from link exchanges.

However, we are *completely* absent from the SERPS of the major keywords which our site is optimized for.

Worth mentioning is the fact that a number of the sites linking to us share the same IP.

Questions:
1. How long is the update cycle of G, i.e - how long does it usually take SERPS to adjust themselves to a website's PR?
2. How can we find out whether we've been penalized?
3. Can there be a 'hidden' penalty, even though we can clearly see our backwards links and we have a "good" (?) PR?
4. Is it a good idea to contact G and query them?

Grateful for your attention,

Pavel.