You could always state, "I may not reply for a while as I'm busy sorting another issue out"
When people respond and the originator of the thread doesn't reply it's assumed that it's abandoned and people don't like there time wasted. Take into consideration 24hrs is a long time on PCAdvisor lots of people come and go, lots of problems are posted and sorted very quickly.
In regards to thankyous, I wouldn't say grovelling thanks but it is nice to get an acknowledgement and to know you helped resolve the issue. Most members would be happy just for the person to tick resolved and state what it was that worked to fix the problem.
Generally I don't like receiving mail but I recieved an email from one guy recently and it was a straight forward thankyou for the help I gave him. It wasn't grovelling in anyway and it was nice to recieve it, it made my day actually knowing that my help was appreciated. I don't think there is anything wrong with saying thankyou, do you?