i'm currently using a growlux 400w hps, which apparantly contains more blue than most other hps, supposedly making it ideal for both veg and flower. i used it for both with no problems at all, though i have no experience of MH.
My friendly local gwowshop tho (who both recommend and sell these bulbs..) suggest you should only use them for 2 grows max.. well, i'm vegging my 2nd and will buy and try a new one (i should keep a spare anyways i guess) before i flower - maybe i'll see a difference there, who knows..