I tested Delicious Library as an audio CD collection manager (I'm not interested in its other functions). Here are my conclusions.

Performance, stability: Tested with sample library on a G4; stable, but annoyingly sluggish.

Interface: Integrates well with Mac OS X, if a bit too eye-candyish; limited customisation.

Database design: Inadequate for any but the most basic of music collections; flaws many to enumerate, from no provision for track data other than title to no provision for credits.

Data export: Limited to tab-separated text; no customising is possible, no explanation of the format provided.

Data import: Direct import from other applications is claimed, but there's no indication as to which those applications might be; iTunes does not appear to be among them. Alternatively, from tab-separated text file; the format is not described anywhere; importing a text file exported by Delicious Library produces strange results (e.g., B.B. King's "Live in Cook County Jail" becomes "1971 Live At Cook County Jail", with different values for label and genres and slightly different values for tracks).

Data input (manual): Through Delicious Library's form -- basic and not customisable, with limited copy/paste capabilities.

Data input (automatic): Very limited -- only from Amazon, by keyword, ASIN, ISBN, or by barcode, which may be scanned by camera or barcode scanner; no support for freedb, CDDB, or any other source, let alone for CD Info.cidb; no scanning of mounted CDs.

Data management: Limited searching capability, enhanced somewhat in Tiger by Spotlight.

Scripting: Very limited AppleScript support; no scripting support for database management tasks.

Other features: Delicious Library has several other features (e.g., voice control, current value vs retail price, cataloguing of books and other media, etc.) which I did not test; IMHO, they do not compensate for its fundamental limitations.

Conclusion: The pre-release version had an excellent review in Ars Technica; but I was very disappointed by Delicious Library. It feels like a souped-up interface to Amazon ("Amazon-at-Home" or "MyAmazon" would have been a more appropriate name). Visually it is very attractive; but everything else is a let-down, from its sluggish performance to the exclusive reliance on Amazon. If my entire library, books included, would have been the kind that fitted comfortably in the average undergrad dorm room, maybe Delicious Library would have been useful. As it is, I classify it under "expensive eye candy".

Alternatives: CDpedia (has its limitations, but it's a much better tool), Music Collector (not tested), InCDius GH (apparently abandoned), CDFinder (a disk cataloguer rather than a collection manager, but it does do audio CDs).