Pat has a good article about Nyjer Morgan's value. UZR is among the best available defensive statistics, so it's easy to be cowed by Morgan's UZR into thinking that Morgan is an otherworldly defender rather than just a very good one, but the thing is that Morgan's UZR is so ridiculous that it's almost impossible he'll sustain it. In fact, since 2005 the only outfielders with a UZR/150 near Morgan's 2009 mark of 28.1 are Andruw Jones in 2005 and Alex Rios, Jayson Werth and Franklin Gutierrez in 2008. Jones was probably the best defensive outfielder of our era, and Morgan doesn't belong in that category yet. Rios and Werth ostensibly took enormous steps backward in 2009 and were average defensive outfielders, at least by UZR/150.
Gutierrez is probably the most telling example. He's widely regarded as a great defensive outfielder. He posted a UZR/150 of 26.9 in 2008, and has posted a 17.6 in 2009. 17.6 runs above average is still great, but I'd think expectations for Morgan next year--assuming he's healthy--should start around there, or maybe a little below. Morgan made huge steps forward this season and he deserves credit for that, but he's not as good as his UZR makes him look.
In addition, as Pat notes, he's probably going to run into what we might call the "Bourn Fluctuation," the script of which was, incidentally, rejected by Universal. Players like Michael Bourn, Willy Taveras and Morgan depend on their batting averages as the basis of their offensive games, and batting averages fluctuate a lot from year to year, so Morgan is, in my opinion, just as likely to have a complete stinker of a season next year as he is to have a good one. Morgan has done a lot this year to change my opinion of him, but I'd still rather have Lastings Milledge.
The Hardball Times lists the greatest moments in the Pirates' 17-year losing streak.
WTM's excellent site is updated for most of the low minors.