There was a news items just a few years ago showing
evidence that the dust disks found around other star
systems are being pushed into interstellar space by the
megatonful every second for ages.

Though you need a subscription to get the full article,
here is the abstract of the relevant paper:

A mechanism for interstellar panspermia

W. M. Napierâ€

ABSTRACT

Metre-sized boulders ejected from the Earth by large impacts are destroyed through collisions and erosion by impacting zodiacal cloud dust particles. The time-scale for such disintegration in a dense zodiacal cloud may be 104 yr. Once reduced to a critical size, the particles are rapidly ejected from the Solar system by radiation pressure. The critical size for ejection is of the order of a micron, large enough to protect groups of micro-organisms within them from solar ultraviolet irradiation. Such life-bearing particles are ejected at a mean rate of 1020 per million years. During passages of the Solar system through or close to dense molecular clouds, a significant proportion of the particles may be incorporated into protoplanetary systems and protected from cosmic rays within growing planetesimals. The specific number density of micro-organisms so deposited is highest in small, dense molecular clouds. On the assumption that this ejection mechanism is common in other planetary systems environmentally capable of supporting life, a 'chain reaction' may seed the disc of the Galaxy within a few billion years. In that case it is unlikely that life originated on Earth.

http://www.blackwell-synergy.com/links/doi/10.1111%2Fj.1365-2966.2004.07287.x