There's a noticeable difference if you spend enough points. However, it's fair to say most groups won't notice where you spent your talent points. Unless you use an ability unique to one tree or another, the primary thing people will notice is how well you do your job; while talents help at doing your job, they don't dictate it.
Let's take one of my favorite spells, Earth Shock, as an example. As a shaman, I use Earth Shock to interrupt enemy spellcasters, so I rely on having it available quickly. Thing is, the spell is on a 6-second recast timer (along with all Shaman shocks). I can pay talent points to reduce the cooldown timer on my shocks by a full second (a long time in WoW). Will my group notice this 5-talent point investment? Almost certainly not. But *I* will notice it, because I'll be able to survive situations that would kill me otherwise. By the same token, the group probably won't notice that I spent points on reducing my shock timers, but they'll notice that I off-tanked the spellcaster add while they dogpiled his buddy.
Talents don't majorly change the face of the game. They do provide those little extra edges that can mean the difference between life and death in questionable circumstances.