I have commented on Infinity before--upstream on either the POD or self-pub thread. I have both completely self-published a book (using a good regional printer) and used Infinity for other books. (My next book, however, is better suited for a commercial market, so I will start querying soon.)
If you can sell over a thousand books, consider complete self-publishing. Working with a local publisher, you can have your book in 6 to 8 weeks. I did. I am now mid-way through my second press run with my self-published novel.
If you can sell at least 200 books, Infinity is a good choice IF you already have a readership in place, your book is of interest to those primarily in your region, you have speaking engagements, school appearances, or other appearances where you can sell your book, etc. You will have your book in hand about 8 weeks after signing the contract.
Infinity is honest, does what it says it will do, has a toll-free number answered by a live person, responds quickly to emails, gives you considerable input in the font & cover design (or you can have them do it--included in the set-up fee) and you can get your rights back with only a few days notice. Infinity does occasionally give discounts on the set-up fee (including a discount for returning authors and discounts for those who have attended particular writers' conferences--won't hurt to call them and ask). You don't need more than their basic service. It does take about 3 months for your book to be on the online book sellers, like Amazon and B&N.
Infinity does about a book a day, according to the author rep, John Harnish. Local bookstores and other shops who already know you are likely to order from Infinity because of the return policy. (Infinity ships these books individually shrink-wrapped, by the way--I discovered that when I stopped in at a shop that carries my books.) Because Infinity prints in-house, it ships out books very fast--I've never waited for more than 5 days; usually I get them in 3. If you order 20 or more books, shipping is free. I usually order 20 at a time for readings. Three regional independent bookstores and three local gift shops order my books directly from Infinity now.
Infinity's cover prices are less than most other PODs--that's a plus. Your first order with Infinity is 50% off cover. Because you get a 10% royalty on what you buy, your price is actually less than half of the cover price. After that, you get 40% off (and royalty).
If you already have a readership and you buy 200 books with your first order, you can hit break-even by the time you sell about 160-170. If you do lots of appearances/readings, you should be able to sell this many in a short time. (Because I have a large rural older readership, many of whom won't buy online, selling them myself works. It won't work for everyone.)
Infinity sends a royalty statement out every month so you know exactly how many copies have been sold. However, they don't send a check until you have accrued $20 in royalties.
Infinity paid for a very nice lunch for its authors at the 2005 Virginia Festival of the Book. They also had our books on display (and for sale) and provided snacks and coffee for us throughout the day.
POD doesn't work for all situations; it isn't a good choice for the blockbuster novel, for example. I doubt it would be good for memoir/autobiography. However, for some niche markets, it can work very well. Yeah, POD is vanity, etc. However, if you write a good book, your readers don't care how you are published. (At least mine don't here in rural America!)
The important thing to remember for POD is, will you be able to make back your investment soon? If you have a strong local readership and a good, fairly-priced book, you can make a profit.
Edited to add: Infinity was sold by its original owners a few years ago and is now no better than the worst of the Vanity Publishers. I no longer recommend them.