Please keep in mind that not everyone has the ability to use 301 redirects.
Case 1 - I'm doing some contracting work at a Fortune 100 company where they use iplanet instead of Apache because of the availability of a support contract. (It's my understanding that a lot of the bigger companies use iplanet instead of Apache for this same reason.) The middleware group there has told me that Iplanet has a limitation of adding URL forwarding only to web sites with home pages in the same server as the iplanet web-server. (They confirmed this with iplanet support.) Iplanet has a screen to use for forwarding that has the server names hard coded into the to and from forwarding fields, so we can't change them.
So for one of the sites I work on there, their middleware group has not been able to find a way to use a server level redirect. We are using a HTML refresh instead, which is causing a loss of page rank. :(
Case 2 - People who have web sites on freebie or cheap web space don't have the ability to use Apache commands. I'm moving a PR6 site with 500+ links from a cheapie web host to a real web space with its own domain name. (I understand I'm an idiot for not moving it long before it got 500 links, but that is beside the point.) The cheapie provider doesn't allow forwarding and has advised me to use an HTML redirect instead.
The old site was content heavy and had quote a few DMOZ links, none of which have been updated after 3 weeks. I don't know when, or if, they ever will be, based on the stories I hear about the DMOZ backlog. :(
I have one page at each of the old pages with a notice that the page has moved and a link to the new page (about 50 pages). I'm hoping that this won't trigger any spam filters as I'm not intending to do anything tricky. But it's going to be a long time before I get all of those links moved pointing to the new site, so I hate to not have forwarding pages in the interim.
If you have any suggestions of better ways to do the forwarding in the above cases to keep Google happy I'd love to hear about them. I understand 301 redirects are best but they just aren't options for me in the cases above.