To say this has no effect is not right, if you spam 1000 guestbooks with one anchor you will see effects no doubt.

You may also get your isp pissed, 100 website owners pissed, and chucked from the G in their new system for getting 1000 irrelevent links in 2 days. But to say it wont help in MSN and yahoo is wrong, unless they have instituted the same boxing as the G, which last I checked they hadnt.

In the end it just will make you look tacky and spammy, so its not worth your energy nor risk.