This article is a good overview of options, with the BIG benefit of not focusing or trying to sell a particular system. Good show :)
With the Tape vs Disk argument, very balanced. I think, however, the "30 years" for tape is a bit generous, considering there have been studies showing that even under ideal conditions, tape degrades and leaves very little data (20% in one study) actually usable after even just 10 years. Combine that with requiring a tape drive (with interface!) that can read the tape. The same argument can be said about hard drives, but ask yourself how many computers still have IDE interfaces and then ask yourself how many computers have Ultra 160 SCSI interfaces (that still work). Not to mention you can get an external IDE USB enclosure whereas a SCSI tape drive equivalent is rare (or non-existent). Basically, the new ($2000+!) tape drives running SAS as an interface likely will still be connectible in 10 years, but I'd be more willing to bet on a SATA protocol. I would also be fairly certain a hard disk drive will last 10 years over a tape, if merely for the robustness and impermeability of the enclosure. For those thinking "flash drives would be awesome!" the answer is no, they wouldn't be. I believe the charge leakage of a flash cell is 5 years. Of course, the wear leveling algorithms of SSDs would move that cell data long before the charge diminishes to unreadability. Backups are meant to be cheap anyway, that's why tapes have lingered for so long. With 1.5TB disks dipping to the $80 mark though, and LTO5 tapes (1.5TB uncompressed, 3TB at the optimal 2:1 compression) at $70, it's almost a no-brainer to get the HDD, especially if your D2D software does compression too (which can get higher than a measly 2:1 depending).
As for types of backups, I personally am using a synthetic full with incremental forever method on D2D. For our archive off-site, we dump a full D2D (hence the need for synthetic fulls). Of course, the thing cautiously avoided in the article is the overwhelming cost of some of these backup methods (such as a tape library). Many small businesses could get away with a rudimentary tape backup system, or better yet, the good-ol' external HDD. Their DBs could be shut down at midnight for a full file-level backup (or sql dumped), and their file server copied. Perhaps an Exchange store exported. However, as far as dedup goes, only the file server would benefit from file-level dedup, and the exchange store and DB would highly benefit from block-level dedup. The more monolithic file stacks (think Sharepoint, SQL Server, VMs, etc) you have, the more block-level dedup can help with your on-disk storage.
I will say this: if the total size of your full backups is over 3TB, your benefit from tape backups significantly improves though :)