I tried the Hoya R72 (77mm) several months back but decided to go with a converted body instead. If you just want to dabble in IR, a filter is probably the way to go, even with its limitations. If you want to get into IR deeper, then a converted camera body is definitely the way to go.
Filter limitations: long exposure times, tripod will be necessary, you may have to compose, focus, and then attach the filter. AF may be ineffective. Also, if foliage is in your pictures, any breeze will cause it to move during the long exposure and will appear OOF in the final image (same for cloud movement).
Converted body: 'normal' exposure times, meter through the lens, AF, a tripod not always necessary.