The guy has been attempting to get 'mainstream appeal' again with his last three albums, by performing with Beyonce and during the Superbowl.
But somehow the (commercial) results were so-so: the albums (and singles) didnt seem to be promoted properly, the hardcore fans complained about the albums being to 'lacklustre' and the music journalists just offered a lot of clichés when reviewing those albums.

Next to that his 'original' approach to selling and promoting his 'art' in general, didnt really seem to pay off.
Planet Earth was distributed for free with an english newpaper, which mostly led to complaints about: when its free, its probably not a good album. And i am sure most of this giveaways are no to be buyed for a bargain at second hand record stores.
His fight against fansites 'using' his material, but also popular sites like Youtube and Videogoogle has set a lot of 'bad blood', not only among his hardcore fans, but also with the general public. The general consensus seems to be his a whining old jerk who cares more about the money, then about the music.

To conclude, what in the beginning (the release of Musicology in 2004) felt as an commercial and artistic comeback, in hindsight comes over as a disaster. To me it feels he has made some of the dumbest decisions (marketingwise) he could have done.
Next to that, musicwise those last three albums may sound more disciplined, less self-indulgent on the surface. But in the end they didnt really connect with the hardcore fans as well as the general public, because Prince most of the time sounded he was holding back, and not truelly being himself.

So, i think 2008 could be a crucial year from him. Most of his hardcore fans surely wont appreciate a new album in the vein of the last three ones, i think. And the general public just couldnt give a damn, probably.
I think his career will suffer more if he releases a Rainbow Children part two type of album or some halfbaken Crystall Ball-like boxset.
He can turn things around when he might release some album like Diamonds and Pearls was, containing at least 3 or 4 songs that have written 'hit' all over them.
Another option is a brand new album that is both innovative and daring as well as commercially appealing: a new Purple Rain or Sign of the Times.

What do you think about 2008? what will be the value of this year for Prince career?