I went ahead and got Netflix (well, just free trial for now) so I could do a marathon viewing of the show. I currently have six episodes left of season 2.
As for the mother, I have a theory on who she is, now I know we've all seen her in the final and know who she is:
If you recall in about the first season, Ted signs up for a dating service that is supposed to match him up with his soulmate. He eventually does get matched up with a girl that is incredibly compatible with him, only he skips out on the date so he can hook up with Robin. I believe we'll find out that this "perfect" girl is in fact the Mother. Something I hope they bring up over the course of the final season.
HIMYM is always been exceptionally good (especially considering it's a com) at this sort of thing.
I got to think Bays and Thomas are scouring every episode looking for every nibblet they can stick into the final season.