Any place where you can post a link back to your site is good.
First, you have the advertisement v alue, people see your site and may go to it. Once there, they may buy from you, use your service, or link to you. the link would help your site.
Second, google does search these sites, although we don't know the value that they put on a Y-Group. Go to a group, make a post and include your web site link. Later do a seach like this: +domainname.com which will return any listings that have to include the text after the + and if you see your site in the Y-Group you have an answer.
Just participating in a group does not help. Using what you learn will help you.
post in any of these, and the search engines will find it.
Post your video here
http://www.AtomFilms.com
http://www.Blip.tv
http://www.Blog.com
http://www.Blogger.com
http://www.BoFunk.com
http://www.Clipshack.com
http://www.Dailymotion.com
http://www.Dave.tv
http://www.Eyespot.com
http://www.Flurl.com
http://www.GoFish.com
http://www.GUBA.com
http://www.IFilm.com
http://www.Livejournal.com
http://www.LiveLeak.com
http://www.LiveVideo.com
http://www.MegaVideo.com
http://www.Motionbox.com
http://www.Odeo.com
http://www.Photobucket.com
http://www.Pixparty.com
http://www.Putfile.com
http://www.Revver.com
http://www.selfcast.tv
http://www.Sharkle.com
http://www.Stickam.com
http://www.SUMO.tv
http://www.Twango.com
http://www.Veoh.com
http://www.Video.google.com
http://www.Video.yahoo.com
http://www.vidilife.com
http://www.Vimeo.com
http://www.vMix.com
http://www.vSocial.com
http://www.Wordpress.com
http://www.Xanga.com
http://www.Yahoo Podcasts
http://www.YouTube.com
http://www.ZippyVideos.com
Community Site List
http://www.Backflip.com
http://www.Blinkbits.com
http://www.Blinklist.com
http://www.Bmaccess.net
http://www.del.icio.us
http://www.Furl.net
http://www.Getboo.com
http://www.Myweb2.search.yahoo.com
http://www.Netvouz.com
http://www.Wink.com
You can advertise here for free:
Yahoo local on yahoos home page
http://www.hits2u.com/
http://goldbizz.localads.co.uk
http://www.trafficswarm.com/
http://www.koolplaz.com/
Post a link to your site for free where it is allowed
Examples are:
http://www.craigslist.com
http://base.google.com
Classifieds for Free http://www.classifiedsforfree.com
Text Link Exchange http://www.txtswap.com/
Recycler.com http://www.recycler.com/
Yahoo Classifieds http://classifieds.yahoo.com/
US Free Ads http://www.usfreeads.com/
Free PR firms
http://www.prleap.com/sign_up.html
http://i-newswire.com/
http://www.24-7pressrelease.com/
http://www.pressbox.co.uk/cgi-bin/links/
http://www.pr.com/press-releases
http://www.prfree.com/
http://www.clickpress.com/releases/index
http://www.theopenpress.com/
http://www.przoom.com/
http://www.prweb.com
http://www.newswiretoday.com/
http://www.free-press-release.com/
Free Classified sites
adlandpro.com http://www.adlandpro.com/
adlandpro.com http://www.adlandpro.com/
adpost.com http://www.adpost.com/
adquest3d.com http://www.adquest3d.com/main.cfm?brd=1
adtrader.co.uk http://www.adtrader.co.uk/postcode_splas...
backpage.com http://www.backpage.com/classifieds/inde...
bestadforum.com http://www.bestadforum.com/
buysell.com http://www.buysell.com/Brand/BuySell/Spl...
caklassifieds.com http://caklassifieds.com/
caklassifieds.com http://caklassifieds.com/
chooseyouritem.com http://www.chooseyouritem.com/
ClassifiedAds.com http://www.classifiedads.com/
classifiedextra.ca http://www.classifiedextra.ca/
classifieds.co.uk http://www.classifieds.co.uk/
classifieds.myspace.com http://classifieds.myspace.com/index.cfm...
classifieds.yahoo.com http://classifieds.yahoo.com/
ClassifiedsForFree.com http://www.classifiedsforfree.com/
classifiedsforfree.com http://www.classifiedsforfree.com/
craigslist.org http://www.craigslist.org/about/sites.ht...
domesticsale.com http://www.domesticsale.com/
domesticsale.com http://www.domesticsale.com/
e-classifieds.net http://www.e-classifieds.net/
economist.com/classifieds http://www.economist.com/classifieds/
epage.com http://www.epage.com/
expo.live.com http://expo.live.com/default.aspx
ezilon.com http://www.ezilon.com/
freeadpost.freeforums4u.com http://freeadpost.freeforums4u.com/
freeads.biztop.com http://freeads.biztop.com/
free-advertising-blog.com/index.php http://www.free-advertising-blog.com/ind...
freeadvertisingboard.com http://www.freeadvertisingboard.com/
FreeAdvertisingForum.com http://www.freeadvertisingforum.com/
freeadvertisingforum.com http://www.freeadvertisingforum.com/
freeadvertisingzone.com http://www.freeadvertisingzone.com/
friday-ad.co.uk http://www.friday-ad.co.uk/
google.com/base http://www.google.com/base
gumtree.com http://www.gumtree.com/
hoobly.com http://www.hoobly.com/
hoobly.com http://www.hoobly.com/
iclads.com http://www.iclads.com/
InetGiant.com http://www.inetgiant.com/
inetgiant.com http://www.inetgiant.com/
isell.com http://www.isell.com/
itsmymarket.com http://www.itsmymarket.com/
kijiji.com http://www.kijiji.com/
la.kaango.com http://la.kaango.com/
livedeal.com http://www.livedeal.com/index.jsp
london.kijiji.ca http://london.kijiji.ca/
loot.com http://www.loot.com/
morefreeadsforum.freeforums4u.com http://morefreeadsforum.freeforums4u.com...
olx.com http://www.olx.com/
oodle.com http://www.oodle.com/
ozfreeonline.com http://www.ozfreeonline.com/
ozfreeonline.com http://www.ozfreeonline.com/
postaroo.com http://www.postaroo.com/ has shut down
postfreeadvertisements.com http://postfreeadvertisements.com/
postyouradforfree.com http://www.postyouradforfree.com/
recycler.com http://www.recycler.com/
salespider.com http://www.salespider.com/
seethisitem.com http://www.seethisitem.com/
sell.com http://www.sell.com/
selloutads.com http://www.selloutads.com/
skelbimai.co.uk http://www.skelbimai.co.uk/
subblurbs.com http://www.subblurbs.com/
tauque.com http://www.tauque.com/
TheFlyer.com http://www.theflyer.com/
thefreeadforum.com http://www.thefreeadforum.com/vbull/
thefreeadforum.com http://www.thefreeadforum.com/vbull/
traderonline.com http://www.traderonline.com/
tytia.co.uk http://www.tytia.co.uk/
uk.freeads.net
uscity.net http://www.uscity.net/
usfreeads.com http://www.usfreeads.com/
vflyer.com http://www.vflyer.com/main/Guest.jsp
villaricaclassifieds.com http://www.villaricaclassifieds.com/
vivastreet.co.uk http://www.vivastreet.co.uk/
webcosmo.com http://www.webcosmo.com/
worldtradeforum.xaviermedia.com