Companies were initially reticent to jump to SP2 when it debuted last year, but the AssetMetrix study found that most companies weren't blocking SP2 entirely; they just had not upgraded in large numbers. Of the 207 companies that were using XP on at least 10 machines, about 40 percent were blocking SP2 universally. At the other extreme, about 8 percent had forced the SP2 on all XP-based machines as a matter of policy.Microsoft suggests corporates to install Service Pack 2 on Windows XP systems, but only after appropriate testing.
More info at CNET