I have had lots of experience with this flying gliders in New England where there is much controlled airspace. I have found that a lot depends on whether you sound (on the radio) like you know what you are doing. If you do, they seem to take the glider traffic in stride. If you sound like you are in crisis mode they will help you - but you are not welcome there as they will likely disrupt all the other traffic to get you in.

A crisp professional initial call up indicating that you have the most recent ATIS information and a statement that you "can follow their traffic" (meaning you don't have to cut in front of somebody) goes a long way toward making you welcome.

Don't ask the tower for anything that might put them "on the spot" (like asking to land in the grass or on a taxi way) and do your utmost to roll clear of the active runway.

Transiting class C airspace with a transponder is now much easier because they will usually let you keep the 1202 code and you don't have to fumble with a new one.

My two favorite experiences were at Aspen CO being sandwiched between a Lear 35 ahead of me in the pattern and a Dash-8 behind me, and at Lebanon NH when we had to land on long distance ferry flight. Both the tug and the glider landed - and they let us launch again out of there.
Great guys in both places.
ROY