I have used mail forwarders for about 12 years now -- starting when I was in the caribbean to do electronic cash development and it took ~6 weeks for mail to get to me, then when I lived on a tiny artificial island off the coast of the UK (Sealand/HavenCo), then with the military at APO/FPO around the world, and other remote sites.
Just forwarding mail adds one level of indirection, which is nice, but being able to scan/email or scan/portal the mail is the killer app -- often forwarding is high cost, high latency, and 90% of mail doesn't need to be forwarded, or if viewed first, can be forwarded with much less time sensitivity. Plus, there are a lot of vendors who ship none (or only some) of their products to APO/FPO/overseas, so being able to reship packages is great.
(there's also the whole cover order issue; basically traffic analysis for mail, without a warrant. Using multiple jurisdictions for this kind of thing might help, but it is irrelevant to many users)
Postal remailers are also great in that they let tiny startups have 24x7 mail coverage, let you appear to be local to a given market, etc. The combination of postal remailers and something like google voice is great for a distributed, small enterprise.