Postgres: VACUUM

Any comments on multi-versioning problem:

As far as I understand from PG documentation, *CURRENTLY* VACUUM must be run
regulary, otherwise:

-Q. database will grow as fast as there are many DML going on it, won't it?

-Q. transaction ID may wrap - no doubt here.

-Q. Good news that VACUUM nowdays can run in parallel with other db activity
(non locking mode) and that pg_vacuum automates execution of VACUUM - this is
so, ins't it?

- Q. Bad knews that VACUUM must eventually scan every row(in fact, every row
and index pages?) in the database(?):
- if this is true(?) then can anyone give an idea on how long it runs
for a paticular size of the database and how much it slowdowns a database?

Thank you in advance,

Laimutis Nedzinskas
Reykjavik, Iceland