I know that most people think that Assassins are horrible. They think, Assassins agro too much, they try to tank when they can't, the nerf of AoD makes the Assassin even worse, etc.
My advise, either start your own party and get people to join (instead of you joining others), or rely on your secondary profession.
My Assassin is A/Rit. I can rely on the restoration or communion aspects of my Ritualist when I go with PUGs. I'll tell the party upfront, that I'll go as a ritualist and use no Assassin skills. They will let me in, either that or I'll join with guildies or friends. Henching is fine for normal quests, but not really for city missions.
If you are a monk, people know you can't heal as well as a Primary Monk, and without bonding skills, you don't have much to offer as a Monk. At least ritualists don't necessarily need to rely on Spawning to get healing or protection spells to be at their best. The recharging sucks, but its the healing/protection aspect that is the key. At least that's what I find.
Groups like core characters, Tank, Nuker, SS, MM, Battery (sometimes), Healing monk. People still frown upon Mesmers though.
I wouldn't be discouraged about not getting into groups as an Assassin, I've been in groups where we had 2 (I wasn't an Assassin then). Usually thats the limit for any group.
Keep up your faith, Assassins will one day be respected in PUGs.