Thanks per se are not necessary IMHO, but feedback would be nice, either to say it worked (with or without the thanks doesn't matter), or to say it didn't. I spent some time yesterday trying to find a solution (hey, I'm on vacation, I have nothing else to do), and the feedback I got helped me to work out where my solution was lacking, and we kept at it until it got done.
I'm a relative newcomer to this board (and compared to most of the people here also relatively new to Excel), and I know my limitations, so I only step in to assist when the answers are in my province. However, I am not always sure that my way is the best way, so feedback that it worked is appreciated. Even if there are four solutions offered and only one is "correct" because that is the one the OP picked to use, the "thanks M1" in Erik's example is useful because one starts to analyse why that solution was better than one's own.
Deviating from the thread slightly, what does the panel think about putting a [solved] or [resolved] before the thread once it is solved/resolved. Sometimes I see a thread with one reply and that has solved the problem. Other times, there are threads with myriads of responses, yet the solution is being developed. I wonder how many would-be responders ignore that particular thread because "its probably been answered by now".
Another slight deviation : In my comparatively short life on the board, I have seen practically the same names crop up time and again on most occasions responding to the problems. What would the panel/moderators/Board think of acknowledging their time and trouble and expertise with another hall of fame, this time giving kudos for the number of solutions, mostly all elegant, that each has given.
Which brings me back to the thread. Thank you all, you know who you are, for the time and trouble you take to assist on the most humble to the extremely mind boggling questions that it has been my fortune to see in any forum. I attend this forum mainly to feed off the crumbs from your tables. If, in passing, I too can feed someone off the crumbs I have collected, I am indeed twice blessed.