You can with 'pv' (
apt-get install pv with Debian and ubuntu). I recommend to monitor the number of files transferred, since the amount of data transferred is not correlated to the size of files but on the delta between the source and destination. And counting files will count the same progress for one big delta and another one with small delta. Which means that in any case the ETA estimation might be far off. The size-based ETA only works if your destination is empty, in this case delta == size of source.
The general idea is to emit one line per file 'transferred' from rsync, and count those lines with 'pv':
rsync -ai /source remote:/dest | pv -les [number of files] >/dev/null
I tend to backup whole filesystems (for several reasons), in this case you can use the much cheaper
df to get the number of files (rather than
find wich will traverse your source hierarchy another time after rsync did it). The -x option appears to make sure rsync stays on the same source filesystem (and does not follow other inner mounts):
rsync -aix /source remote:/dest | pv -les $(df -i /source | perl -ane 'print $F if $F =~ m:^/:') >/dev/null
If you want to count files in /source in a general way, use
find /source|wc -l (warning again: might be slow and heavy on I/O).