Since domain purchasing has become a major part of SEO (some would say it always has been), and considering how valuable expiring domain names can be, I figured dredging up Mike Davidson's old post on the subject was worthwhile:

So if domains are available to the general public 75 days after they expire, how do you know your GoDaddy backorder isn’t one of many other backorders from other people using other services? The answer is, you don’t....

...So I decided to enlist the services of all three major domain snatching firms in hopes that a) one would grab my domain for me, and b) no one else would be competing against me.

The three services — Snapnames.com, Enom.com, and Pool.com — all operate in a similar manner. They use a network of registrars to hit the Verisign servers at frequent intervals (but not too frequent to get banned) and snatch as many requested names as possible. If you don’t get your name, you don’t pay. But that’s where the three services begin to differ...

The more SEO-friendly way to acquire a domain is to buy it directly from the owner before it lapses (which costs considerably more). In order to do this without being detected and potentially sandboxed by Google, you'll need to retain all the registrant information and have an external legal contract stating you own the site. Once you've re-pointed it to your servers, changed out the content to your needs and maintained your rankings for several months, you can go ahead and start to change small registration details one-by-one (technical contact, address, etc.). This process was more fully explained by Jim Boykin.

If anyone else has great expiring domain advice, we'd love to have you share.