Hot pink roses are perfect for the type of relationship where you've known each other for a while and are ready to gently move toward something more serious, without being overly passionate too early.  They're not as "full-on" as the romantic red roses, but can give an inoffensive hint of heading in that direction, without the risk of harming a good frienship.  If your partner or intended one isn't interested in advancing to the next stage of a relationship, you've always got the protection of the fact that these roses are, after all, still just pink and not the glaringly obvious romantic red, and if the fact that they're hot pink roses is questioned (rather than paler pink) you can always say that they were simply the better looking of all the pink roses you could find, and you thought that your friend deserved the best.
In the language of roses, their meaning is very much similar to that symbolized by their lighter cousins, the pale pink roses.  You may therefore be asking: What do pink roses stand for?  Traditional rose symbolism says that pink roses in general signify appreciation and admiration of a person.  They are a sign of happiness and also are given as a Thank You gift.  Conversely they can be used to symbolize sympathy, but pale pink roses are probably better to demonstrate sympathy than these hotter pink flowers.
An ideal example of effectively using these rose types would be on your girlfriend's (or good friend's) passing of exams, a driving test or some similar occasion.  These are most certainly joyous events, so the symbolic happy significance of pink roses would fit perfectly.

Flowers can be the best gifts for a birthday of someone special too, and hot pink roses can aid you in expressing your happiness for the day.  At the same time they give a way of showing your gratitude for a good friendship, and your admiration for the recipient without the pressure that red roses would give.