Bringing a bouquet of flowers to a social engagement is not, repeat, not old fashioned. It is, in fact, just the thing.
It is not necessary to limit oneself to a bouquet of cut flowers; arrangements in vases and potted plants are also quite welcome, especially if you are not the only guest. If you arrive at a party with a cut flowers wrapped in tissue paper, do not expect them to end up prominently displayed in the middle of the dining room. The host and hostess are likely to be far to busy to have the time to take your flowers, re-cut the stems, find a vase, arrange them suitably and put them out for the admiration of others. The host and hostess are just trying to get the food out, the drinks poured and the seating plan in some order. If you want your bouquet turned into an arrangement, offer to do it yourself.
If you are going to bring an arrangement of cut flowers and you actually take the time to do it ahead of time, then this might be an excellent time to recycle on of those cheap vases that you got when someone brought an arrangement of cut flowers directly from the florist to your house. While generally not hideous, they are usually not something you would buy yourself. You can’t bear to throw them out and yet you already have plenty of your own vases. So go to the florist on the way home, re-arrange the flowers in the old florist vase, get dressed and go to the party.
At a listserv called MacRumors someone called “Leareth” in Vancouver asked what to bring to dinner at friends house. He usually brought wine, but these friends did not drink. The first response was “A potted orchid”. The next two respondents mentioned flowers, but also potted English ivy. Other posters mentioned cut flowers and even specific flower types (Anthurium), but in the end Leareth stubbornly went with ice wine, reasoning that because so little was consumed at a sitting that non-drinkers would drink it, but also included a small pot of herbs to go with a bottle of balsamic vinegar.
The orchid and the ivy define one end of the potted-plant-gift spectrum, which includes those specimens that stand a chance of becoming more or less permanent parts of your host/hostess’s household. The pot of herbs falls closer to the other end of the spectrum, which includes Easter lilies, poinsettias and cyclamen. All of the latter tend to have a half-life. The herbs can potentially persist for months with a certain amount of care and harvesting. The foliage of lilies and the cyclamen inevitably withers a few months after flowering after enough nutrition has been stored in the roots. Real plant people will be able to coax these specimens into the next season, but most mere mortals will chuck them.
The potted plants or pre-arranged arrangements are both safe and polite routes when you do not know the hosts well. In many discussions on-line a schism formed that seemed somewhat along generational lines. I.e., younger people are less formal. The older generation may have a problem with company barging into the kitchen with a fistful of flowers and merrily offering to re-cut, re-arrange the flowers in a vase that they hunt down themselves in the hosts’ cupboards.
If these are old college friends with whom you have shared a hundred twenty-something-era pizza and beer parties that erupted rather spontaneously, then they might be rather charmed when they have invited you over for a prepared meal and you show up, rather improbably, with flowers in hand.