Autovacuum daemon functionality questions

Hi,

I'm using PostgreSQL 8.2.

I want to configure autovacuum daemon process in our production server in an
efficient way and take advantage of this daemon to perform vacuum and
analyze more aggressively.

I also read about autovacuum daemon at
http://www.postgresql.org/docs/8.2/interactive/routine-vacuuming.html

My questions are:
1. Why need to have 2 parameters (base threshold and scale factor) to define
the threshold value, when either one of the parameter is more than enough to
define the threshold value. Can you explain the significance of having both
parameters. What is the real-time advantage of this?
2. Documentation says ".... If the number of obsolete tuples since the last
VACUUM exceeds the "vacuum threshold", the table is vacuumed ...".
I also know about this table "pg_stat_user_tables" which has columns
n_tup_ins, n_tup_upd, n_tup_del, last_autovaccum and last_autoanalyze.
Since INSERT, UPDATE and DELETE count gets incremented everytime and do not
reset after running autovacuum/autoanalyze, how does autovacuum identifies
obsolete tuples since last VACUUM from this entries.
3. Is there a way to see autovacuum daemon log entries?