Summary and Info:

When parenthesis are part of the descriptions accompanying the optdepends, makepkg throws an unexpected EOF error. This error happens with pacman 3.5.0-1 in testing. The pacman from core isn't affected.

To reproduce:
PKGBUILD:
========
pkgname=foo
pkgver=1
pkgrel=1
pkgdesc=""
arch=('i686' 'x86_64')
url=""
license=('GPL')
optdepends=('vdpau-video: VDPAU backend for VA API (for GPU acceleration on Nvidia cards)'
'libpulse: PulseAudio support')
source=()
md5sums=()

package_() {
cd "${srcdir}"
true
}
==============

makepkg output:
==============
$ makepkg -f
/usr/bin/makepkg: eval: line 1279: unexpected EOF while looking for matching `)'
==> Making package: foo 1-1 (Thu Mar 17 01:24:44 EDT 2011)
==> Checking runtime dependencies...
==> Checking buildtime dependencies...
==> Retrieving Sources...
==> Extracting Sources...
==> Removing existing pkg/ directory...
==> Entering fakeroot environment...
/usr/bin/makepkg: eval: line 1279: unexpected EOF while looking for matching `)'
==> Creating package...
-> Generating .PKGINFO file...
-> Compressing package...
==> Leaving fakeroot environment.
==> Finished making: foo 1-1 (Thu Mar 17 01:24:45 EDT 2011)
=======================

Note that if vdpau-video is the last item in the arrary there is no error message. The metainfo in .PKGINFO doens't seem to be affected, at least with this test case.