In the 2008 National League, batters don't fare as well against relievers as they do against starters. This shouldn't come as a surprise--batters only see relievers once; relievers can throw harder in their shorter stints; and many relievers are called upon because they are well-suited to retire one or more of the batters they are going to face.
More specifically, the average NL batter hits 258/329/408, for an OPS of 738. Against relievers, he manages only 244/325/379, an OPS of 704. It's not an enormous difference, but it's noticeable, and it's not a fluke. In 2007, league average was 757 and average vs. relievers was 724--almost an identical difference.
Of course, the next logical step is to look at the Brewers by this measure. By OPS, the Brewers have the 6th best offense in the league, at 750. Against relievers, they are tied for 8th with the Rockies at 696. In other words, our OPS versus relievers is about 20 points lower than you'd expect it to be.
This does raise something of a chicken-and-egg issue. Relievers aren't all the same (thank you, Captain Obvious). In close games, we're likely to see the best relievers a team has to offer; in blowouts, we get the worst. Anecdotally, it seems like the Brewers have played a disproportionately high number of close games this year, suggesting that the relievers we're seeing are of higher quality than average.
(The other team that springs to mind, the Braves, offer something of a counterpoint. Despite losing more one-run games than a soccer team, the Braves are right about average, hitting relievers with an OPS about 30 points lower than their average OPS.)
It's always tough to compare one year's team to another, but there is a lot of continuity between the '07 lineup and the '08 lineup. It turns out that the '07 Brewers, much like the '08 Braves, are almost exactly average in this regard. 785 overall OPS, 750 OPS versus relievers.
You might also be interested to know how individual Brewers are doing against relievers. The laggards are Hardy, Hall, and Cameron, while Fielder is the only guy with a lot of ABs who is hitting well. (That surprised me, since he's the one guy who often results in a pitching change for the opposition.) Here's the complete report.
I suspect this, like most splits, will even out before long. But more importantly, if we're going to talk about it (which seems like a foregone conclusion), we need to have our numbers straight. The Brewers are about average against relievers, and the difference between their vs-relief numbers and their overall performance is a little worse than average. Like the variety of "clutch" stats I touched on yesterday, it's probably not a cause for concern.