I can't bring myself to have a strong opinion either way on the Mark Teahen trade. Teahen was a decent player who was probably more popular with the fans than his numbers deserved, thanks to his media-friendly personality and willingness to be shuffled from third base to right field to left field back to third base, with a little first base thrown in there too (and I'm not qualified to judge this, but The Amazing Michelle assures me his looks did not hurt his popularity, either). Unfortunately, the way baseball salaries work, if a player can stick around long enough, his salary will keep going up, no matter what his production is. And Teahen was likely to get an arbitration-induced raise to around $5 million for 2010.
I like Teahen, but his OPS+ numbers the last three seasons are 98, 91, 94. The average major leaguer's salary is around $3 million. The Royals can't afford (and shouldn't want) to pay almost twice the average salary for slightly below-average production.
As for the players the Royals got back, third baseman Josh Fields and second baseman Chris Getz, I can't decide if these guys are useful or not. Fields will turn 27 in December; Getz turned 26 in August. Theoretically, their careers should be peaking now, so that's good. Fields had a decent rookie season in 2007, but has struggled since. From the stats, Getz appears to be a good-field, no-hit guy with good baserunning skills. Let's face it, the Royals could use some good fielders and some good baserunners, so he may be useful if he can get on base.
Of course, the unanswered questions after this trade involve Alex Gordon and Alberto Callaspo, who appeared to be set at third and second, respectively, in 2010. Perhaps the Royals intend to move one or both players, either to another position or another team entirely.
Until we see what other moves the Royals have in store this winter, it's hard to decide how to feel about this move. If the Royals have traded Teahen for two role players or organizational depth (admittedly, something the Royals need), it's probably not a major move. If one or both players end up starting next April, then the Royals may have pulled off a steal. If they have moved one slightly below-average player for two well below-average players, well...that's not really progress, is it? In fact, it's the kind of deal that has helped put the Royals in their current predicament.