R help - Sep 2006 - counting process form of a cox model (cluster(id))?

Hi,

I am currently analysising a counting process form of a cox model allowing for
the inclusion of time dependent covariates.  An example model I have fitted is

modlqol<-coxph(Surv(Tstart,Tstop,cens.time)~tmt.first+risk
+lqol+cluster(id),data=cat)
summary(modlqol)

My question is quick.  I am looking at 1 event (death), and repeated
measurements (the time dependent covariate 'lqol') are frequently taken
on a subject, so I assume that measurements on the same subject will be
correlated.  For this reason, I included the cluster(id) term in the model. 
However, on p70 Therneau and Grambsch, it states

'one concern that often arises is that observations on the same individual
are correlated and thus would not be handled by standard methods.  This is not
actually an issue. .......................'

so, does anyone recommend that I include the 'cluster(id)' term or does
this only need to be utilised in the situation where there is multiple events
(eg in the bladder cancer study by Wei, Lin and Weissfeld) ?

I appreciate any help on the matter,

Thanks,

Zoe