More information about minima et al. regarding HGS (HUD) system capabilities including what was bought by Alaska Airlines can be found at:
http://www.awgnet.com/shownews/day1/hardwr10.htm
A quick summary:
Can fly Cat-IIIa ops down to 700 RVR and DH 50. Provides rollout guidance upon landing... and can provide takeoff guidance for as low as 300 RVR as well as lower landing minima at Type I ILS facilities, according to the article.
Total HGS system weight: about 60 pounds / 27 kgs for a cost of about USD $500,000.
Seems like at this time, such equipment would be real nice but likely more useful for routes that are frequently solid IFR, potentially with additional qualifying local conditions(?). That sounds like some of Alaska Airlines' routes in the less populated areas of Alaska such as arctic ops (Barrow, AK -- typically cloudy due to land/water thermal evaporation cycle).