def selectRandomComponents(coll, percentage, cmpType = 'ask'):
    allComponents = {
        'edges':[x for obj in coll for x in obj.ActivePrimitive.Geometry.Edges],
        'points':[x for obj in coll for x in obj.ActivePrimitive.Geometry.Points],
        'faces':[x for obj in coll for x in obj.ActivePrimitive.Geometry.Facets]
    }
    cmpTypes = allComponents.keys()
    if cmpType == 'ask':
        cmpType = cmpTypes[ XSIDialog.ComboEx('Component type?',cmpTypes,2) ]
    
    sample = get_random_percentage(allComponents[cmpType], percentage)
    xsi.SelectObj(sample)

def selectRandomObjects(coll, percentage):
    sample = get_random_percentage(coll, percentage)
    xsi.SelectObj(sample)


def main():
    selectComponents = (
        XSIUIToolkit.Msgbox(
        "Select components? YES = components NO = objects",
        c.siMsgYesNo+c.siMsgQuestion,
        "Random Selector" ) == c.siMsgYes
    )
    percentage = float(xsi.XSIInputBox(
        "What percentage to select?",
        "Selection percentage?",
        50 # default %
    ))
    if selectComponents:
        selectRandomComponents(xsi.Selection, percentage)
    else:
        selectRandomObjects(xsi.Selection, percentage)

main()

def evenPositions(crv, quantity):
    '''
    Get an amount of evenly spaced positions on a given curve.
    '''
    subcrv = crv.ActivePrimitive.Geometry.Curves(0)
    percs = [num for num in frange(0.0, 100.0, 100.0 / quantity)]
    percs.append(100)
    ppos = [ subcrv.EvaluatePosition( subcrv.GetUFromPercentage(percs[i]) )[0] for i in xrange(len(percs)) ]
    return ppos

def main():
    size = float( Application.XSIInputBox("What particle size do you plan on using?", "So I know the spacing...", 1) )

    newCurves = []
    si.OpenUndo("Make evenly spread linear curves")
    for crv in si.Selection:
        quantity = int(crv.ActivePrimitive.Geometry.Curves(0).Length / (size*2.0))
        positions = evenPositions(crv, quantity)

        positions = ["(%s,%s,%s)" % (a.X,a.Y,a.Z) for a in positions]
        newCurve = si.CreateCurve( 1, 0, ",".join(positions), False)('Value')

        newCurve.Name = crv.Name+'_evenlySpaced'
        newCurves.append(newCurve)
    si.SelectObj(newCurves)
    si.CloseUndo()

main()

        gatorOp = xsi.ApplyGenOp("Gator", "", targetMesh.FullName+";"+sourceMesh.FullName, 3, "siPersistentOperation", "siKeepGenOpInputs")(0)

        srcEnv = sourceMesh.Envelopes(0)
        srcEnvProp = (p.Target2 for p in srcEnv.InputPorts if p.Target2.Type == "envweights").next()

        env = xsi.TransferClusterPropertiesAcrossGenOp(targetMesh.FullName+"."+targetMesh.Type+".TransferAttributes", targetMesh, srcEnvProp, "Envelope_Weights")
        freezeMe.append(gatorOp)

    xsi.FreezeObj(freezeMe)
    xsi.LogMessage("Gatored %s's envelope to ---> %s" % (sourceMesh.FullName, selected.GetAsText()), 4)

# TODO:
# Middleclick for continuous picking, left click for single.
# Offer to purge unused deformers

            n = len(zeroWeightDeformers)
            if n > 0:
                xsi.RemoveFlexEnvDeformer( o.FullName +';'+ ','.join(zeroWeightDeformers), False )
                xsi.LogMessage( 'REMOVED '+str(n)+' unused deformers from '+o.FullName )
            else:
                xsi.LogMessage( 'There are NO UNUSED DEFORMERS in the envelope for %s' % o.FullName, 4 )
    xsi.LogMessage( "Took %s seconds to purge unused deformers." % (clock() - c), 16 )

purgeUnusedDeformers(xsi.Selection)

You can find Comet's script in this zip of his tools:
http://www.comet-cartoons.com/MELfiles/cometScripts.zip
but if you use Maya 2011, you'll need this specific version of Comet's SaveWeights script:
http://s3.darkvertex.com/hlinked/4forums/cometSaveWeights_Maya2011.zip
** CometSaveWeights FORMAT spec:
The file looks like this:
    [WEIGHTS]
    [COMPONENT]
    objName.vtx[vertexID]
    worldPosX worldPosY worldPosZ
    localPosX localPosY localPosZ
    [END-WEIGHTS]
    [JOINTS]
    jointName1
    jointName2
    jointName3
    ...
    [END-JOINTS]
    // Comments look like this.
"""

from time import clock
from win32com.client import constants as c

xsi = Application
lm = xsi.LogMessage
start_time = clock()

for obj in list(xsi.Selection):
    lm( obj.FullName )
    env = obj.Envelopes(0)
    deformer = env.Deformers
    weights = env.GetWeights2()
    points = obj.ActivePrimitive.Geometry.Points
    oTrans = obj.Kinematics.Local.Transform


    filepath = XSIUtils.BuildPath(xsi.ActiveProject2.Path, "WEIGHTS__%s.txt" % obj.Name)

    cometFile = open(filepath, 'w+')
    cometFile.write("// [WEIGHTS] ")


    oPBar = XSIUIToolkit.ProgressBar
    oPBar.Maximum = points.Count
    oPBar.Step = 1
    oPBar.CancelEnabled = True
    oPBar.Caption = "SAVING ENVELOPE/SKIN WEIGHTS:"
    oPBar.Visible = True

    more = ""
    for i in xrange(0, points.Count):
        oPBar.StatusText = "Vertex #%s" % i
        if oPBar.CancelPressed:
            break

        more += "[COMPONENT] %s.vtx[%s] " % (obj.Name, i)

        oLocalPos = points(i).Position
        more += "%s %s %s " % (oLocalPos.X, oLocalPos.Y, oLocalPos.Z)
        oGlobalPos = XSIMath.MapObjectPositionToWorldSpace(oTrans, oLocalPos)
        more += "%s %s %s " % (oGlobalPos.X, oGlobalPos.Y, oGlobalPos.Z)

        for d in xrange(0, deformer.Count):
            # In XSI weights are 0 to 100, but in Maya, weights go from 0 to 1, so...
            mayaWeight = ( float(weights(i)[d]) / 100 )
            if mayaWeight > 0.0:
                more += "%s %s " % (deformer(d).Name, mayaWeight)
        more += " "
        cometFile.write(more)

        more = ""
        oPBar.Increment()
    oPBar.Visible = False

    cometFile.write( "[END-WEIGHTS] [JOINTS] %s [END-JOINTS] " % " ".join([item.Name for item in deformer]) )


timeTaken = clock() - start_time
comment = "Exported %s points in %s seconds. (Speed: ~%s points/sec)" % (points.Count, round(timeTaken, 3), round((float(points.Count) / timeTaken), 3))

lm(comment)
cometFile.write("// "+comment+" ")
cometFile.close() # Done! :D


# Look out on http://darkvertex.com/ for the pretty plugin edition someday, maybe.